于体温不熔化，但易吸潮，对黏膜有一定刺激性基质是（）。
A、甘油明胶
B、聚乙二醇
C、半合成山苍子油酯
D、香果脂
参考答案：B
将5个不同的小球放入编号为1，2，3，4，5的5个盒子中，恰好有一个空盒的放法一共有______种．
John agreed to the suggestion that his students ________ two weeks to prepare for the exam. [ ]
A. give
B. should give
C. be given
D. would be given
