One important outcome of the work on the expression of genes in developing embryos is sure to be knowledge that can help preventing birth defects. Just as promising (26)
is the possibility of unraveling the complicated writing (27)
of the brain. A mechanic gets valuable insight how an (28)
automobile works by rebuilding car engines; similarly, neuroscientists can learn how the brain functions from (29)
the way it is put together. The next step pursuing the (30)
goal is to find out how the blueprint genes, the home box genes, control the expression of other genes that create the valves and piston of the working cerebral engine. The protein encoded by the latter genes could change the (31)
stickiness of the cell surface, the shape of the cell or its metabolism to create the characteristic peculiar to, say, neurons or neural-crest cell. Surface proteins may be the (32)
mechanism, whereby similar programmed cells stick together to form specific structures; they might also sense (33)
the local environment to help the cell decide what is to do. Clarifying those mechanisms will engage the best talents in (34)
embryology and molecular biology for some times to come. (35)
What is perhaps the most intriguing question of all is if the brain is powerful enough to solve the puzzle of its own creation.

答案:
26.preventing改为prevent
27.complicated改为complexion 
28.sight后加into
29.neuroscientist改为a neuroscientist
30.pursuing后加in
31.later改为latter
32.similar改为similarly
33.去掉is
34.times改为time
35.if改为whether

 
Vitamins, like minerals, are chemicals. There is absolutely not difference in the chemical structure (26)
of the nature vitamin C and the chemical structure (27)
of the synthetic vitamin C. Also, while most sub- stances are harmless at very low level of intake, all (28)
substance -- even the elements that are essential to life -- can be dangerous if you overdo them. Take water for example. Six or eight glasses a day will keep your body in good fluid balance. But you can also be drown (29)
 in it. Some people argue that individuals vary greatly (30)
 in their need for nutrients, it cannot necessarily be stated any given amount is too much; that is all (31)
relative. But since there is little solid information on what is the optimal intake of any essential nutrient in healthy individuals, it would be impossible to give guidelines that take these proportional needs into the (32)
 account. Just as with other drugs, the relation to (33)
 different vitamin dosages varies, with some people better able than others to tolerate large amounts. While we do know that very specifically what the toxic level (34)
 is for vitamins A and D, we are far less sure about vitamin E, even though it, too, is fat-soluble, and we still don’t understand the water-soluble vitamin, the C (35)
 and the B groups, which the body cant store.

答案:
26.not改为no
27.nature改为natural
28.at后加a
29.去掉be
30.that后加 
31.stated后加that 
32. 去掉the
33. relation改为reaction 
34.去掉that
35. vitamin改为vitamins

The telephone system is a circuit-switched network. For much of the history of the system, when you placed (26)
a call, you were renting a pair of copper wires that ran continuously from your telephone to the other party’s phone. You had excluding use of those wires during the (27)
call; when you hung up, they were rented to someone else. Today the transaction is more complicated. ( your call may well possess a fiber-optic cable or a satellite with hundreds of other calls), but more conceptually the system (28)
still works the same way. When you dial the phone, you get a private connection of one other party. This is an alternative network architecture called (29)
packet switching, in which all stations are always connected to the network, but they receive only the messages addressed to them. It is as if your telephone was always tuned in to (30)
thousands of conversations going on the wire, but you (31)
heard only the occasional word intended to you. Most (32)
computer networks employ packet switching, because it is more efficient than circuit switching when traffic is heavy. It seems reasonable the existing packet-switched (33)
network will grow, and new one may be created; they could (34)
well absorb traffic that would otherwise go to the telephone system and thereby reduce the need for telephone numbers. (35)

答案:
26.much改为most
27.excluding改为exclusive 
28.more 
29.This改为There
30.was改为were 
31.going后加by
32.to改为for
33.reasonable后加that
34.one改为ones
35.need改为demand 

The German poet and polymath Johann Wolfgang von Goethe pondered the question of how organisms develop in his scientific studies of form and structure immature plants and animals, a field he found and named morphology. His search for a single basic body plan (26)
across all life-forms led him to think about the prevalence of repeating (27)
segments in body structures. The spinal columns of fish, reptiles, (28)
birds and mammals, for instance, all are made of long strings of (29)
repeated vertebrae. Among invertebrates the growth of virtually identical segments is how striking: in earthworms, for example, even (30)
internal organs are repeated in serial segments. Likewise, the abdomen of flies and other insects are segmented, as are the (31)
successive wormlike articulations in crabs, shrimps and other crustaceans. To Goethe the evidence suggested that nature takes a building-block approach to generate life, repeating a basic element (32)
again and again to arrive at a complicated organism. The only glaring (33)
hole he could see in the theory was the apparent lack of sort of (34)
segmentation in the vertebrate heads. In 1790 he hypothesized that (35)
spinal vertebrate is modified during the development to form the skull.

答案:
26.found改为founded
27.repeating改为repeated
28.fish改为fishes
29.made后加up
30.去掉how
31.abdomen改为abdomens
32.generate改为generating
33.complicated改为complex 
34.heads改为head 
35.is改为are