Q27:

Rye sown in the fall and plowed into the soil in early spring leaves a residue that is highly effective at controlling broad-leaved weeds, but unfortunately for only about 45 days.  No major agricultural crop matures from seed in as little as 45 days.  Synthetic herbicides, on the other hand, although not any longer-lasting, can be reapplied as the crop grows.  Clearly, therefore, for major agricultural crops, plowing rye into the soil can play no part in effective weed control.

The argument is most vulnerable to the objection that it fails to

1. consider that there might be minor, quick-growing crops that do mature in 45 days or less
2. identify any alternative method of weed control that could be used instead of the method it rejects
3. distinguish among the various kinds of synthetic herbicides
4. allow for the possibility of combining the two weed-control methods it mentions
5. allow for the possibility that plants other than rye, handled the same way, might have the same effect

答案是D，为什么？选A吧？