题目

It's my    time to come to the bookstore this month because most of the books in it are my favorite.     A. forth          B. four                  C. fourth 答案：C如果有15个初级卵母细胞，5个初级精母细胞，它们都正常发育并受精，最多能形成的受精卵数目是A. 20个B. 15个C. 10个D. 5个