选到一个好的个体后，需要（）才可以通过自交达到99%纯合。
A.三代
B.五代
C.八代
D.十一代
参考答案：B
For a futures trade:()
A. a single price is determined by supply and demand.
B. the seller receives the bid price; the buyer pays the ask price.
C. the purchase of the asset is at a negotiated price.
火灾发生后，扑救人员应做到什么？
