题目

You won't find paper cutting difficult _____you keep practicing it. A . even if B . as long as C . as if D . ever since 答案：B在有丝分裂过程中，DNA含量相同、染色体数目不同的时期是 [　　] A．间期和末期B．后期和末期 C．中期和后期D．前期和中期