人的精子中有23条染色体,则人的神经细胞、初级精母细胞、卵细胞中分别有染色体多少条[ ]
A.46、23、23
B.46、46、23
C.0、46、0
D.0、46、23
答案:B
212. We must make sure that all the boxes should__________the owners’ names.
A.write
B.be written
C.mark with
D.be marked with
Why do you insist on buying a car ______ you have such good public transportation here?
A.because
B.unless
C.when
D.though