监考to invigilate an exam明天全体学生考英语,他将担任监考.Tomorrow he will supervise all the pupils taking the English examination.在主考监考时任何学生想作弊都是冒险.Any student who tries to cheat while the examiner is watching is playing with fire....
The hydroxyl groups can be changed into esters , ethers , acetals and ketals, etc.最常用的羟基保护基可归纳为三类:酯类 、 醚类和缩醛或缩酮类.Eight acetals ( Ketals ) were synthesized under the optimal conditions.在最佳条件下,合成了八个缩醛 ( 酮 ) 化合物.The yields ...