大肠杆菌分裂一代需要的时间（）
A.18小时
B.20分钟
C.72小时
D.60分钟
E.20秒
参考答案：B
Tom needs some help ________ his homework. Can you help ________? [ ]
A. to; he
B. with; him
C. to; his
D. with; his
正常幼苗类型包括：（）型，带有（）幼苗，（）幼苗。受伤重的不算正常幼苗。
