在光学显微镜下所观察到的细胞结构称为()。
A.显微结构
B.超微结构
C.亚显微结构
D.分子结构
E.微细结构
参考答案:A
下列运算正确的是[ ]
A.a5×a5=2a5
B.a5+a5=a10
C.a5×a5=2a10
D.a5×a5=a10
Scientists say it still needs five or six years _____ it is possible for human patients to take this medicine. [ ]
A. since
B. before
C. after
D. when