Little Tom admitted _____ in the examination, _____ that he wouldn’t do that in future.

A．to cheat; to promise

B．cheating; promise

C．having cheated; promising

D．to have cheated; promised

实验室里将粗盐制成精盐的过程中，在溶解、过滤、蒸发三个步骤的操作中都要用到玻璃棒，分别说明在这三种情况下使用玻璃棒的目的；

（1）溶解时                                                   

（2）过滤时                                                   

（3）蒸发时