某弱酸性药在pH为5时约90%解离,其pKa为()
A.6
B.5
C.4
D.3
E.2
参考答案:C
The man had expected to see all his relatives when in hospital,but______,came to see him while many
of his friends offered him their help. [ ]
A. anyone
B. no one
C. someone
D. none
一端装有定滑轮的粗糙斜面体放在地面上,A、B两物体通过细绳连接,并处于静止状态(不计绳的质量和绳与滑轮间的摩擦),如图所示.现用水平力F作用于物体B上,缓慢拉开一小角度,此过程中斜面体与物体A仍然静止.则下列说法正确的是( )
A.水平力F不变
B.物体A所受斜面体的摩擦力一定变大
C.物体A所受的合力力不变
D.斜面体所受地面的支持力一定不变