性交中断法避孕的缺点是()
A、易造成生殖道感染
B、造成性交中断,影响性伴双方的性满足
C、精液排除体外,易致环境污染
D、易致避孕失败
参考答案:B, D
I____ think there_____be more buildings in two years. [ ]
A. don't ; will
B. /; won't
C. will;don't
D. won't;/
试比较F+菌株与F-菌株接合以及Hfr菌株与F-菌株接合的不同。