奠定近代化学基础的是 [ ]
A.火的发现和利用
B.原子论和分子学说的创立
C.元素周期律的发现
D.钢铁的冶炼
答案:B
My sister met him at the Grand Theater yesterday afternoon, so he ________ your lecture.
A.couldn’t have attended
B.needn’t have attended
C.mustn’t have attended
D.shouldn’t have attended
的负逻辑形式为()。
A.A
B.B
C.C
D.D