（）一般是和硫酸共同灼烧分解为金属硫酸盐后，用重量法测定。
A、硫醇
B、磺酸
C、磺酸盐
D、硫醚
参考答案：C
--- What do you think of receiving and giving gifts?
--- I think the art of receiving a gift is _____ than the art of giving.
A．much more difficult
B．very more difficult
C．much difficult
D．as difficult as
如图所示，重4N的物体A，被平行于斜面的细线栓在斜面的上端，整个装置保持静止状态，倾角为30°的斜面被固定在测力计上，物块与斜面间无摩擦，装置稳定后，当细线被烧断物块正在下滑时与静止时比较，测力计的示数
A．增加4N
B．减少3N
C．减少1N
D．不变
