Which of the following most logically completes the argument below?

Using broad-spectrum weed killers on weeds that are competing with crops for sunlight, water, and nutrients presents a difficulty: how to keep the crop from being killed along with the weeds. For at least some food crops, specially treated seed that produces plants resistant to weed killers is under development. This resistance wears off as the plants mature. Therefore, the special seed treatment will be especially useful for plants that ______.

• Aproduce their crop over an extended period of time, as summer squash does  
• Bproduce large seeds that are easy to treat individually, as corn and beans do  
• Cprovide, as they approach maturity, shade dense enough to keep weeds from growing  
• Dare typically grown in large tracts devoted to a single crop  
• Eare cultivated specifically for the seed they produce rather than for their leaves or roots