He was ______ medical student before he turned _______ engineer.
| A．a; an | B．the; the | C．a; / | D．/; an |
custom
| A．measure | B．upstairs | C．respect | D．sugar |
salt
| A．almost | B．calm | C．chalk | D．half |
singer
| A．single | B．language | C．stronger | D．bringing |
realize
| A．pyramid | B．responsibly | C．whisper | D．title |
The book, ___________ is green, has been lent to my brother.
| A．of which cover | B．the cover of which | C．whose covers | D．its cover |