第一节 ：单项填空(共15小题；每小题1分，满分15分)
21．Generally speaking , _______ according to the directions , the drug has no side effect.
A. when taking B. when taken C. when to take D. when to be taken
22. It was in that house _________ he used to live _____ the secret meeting was held.
A. where ; where B. that ; that C. what ; where D. where ; that
23. After graduation he _______ engineer.
A. became B. was C. turned D. turned into
