若半径为4和5的两圆相外切，则两圆的圆心距是[ ]
A.18
B.9
C.2
D.1
答案：B
检查固体有机物纯度时，一般通过测量有机物的 （）
A.沸点
B.密度
C.折光率
D.熔点
E.比旋光度
The light of this room was _____ dim (昏暗的) for Tom _____ read last night.[ ]
A. too; to
B. enough; to
C. too; not to
D. so; that
