Scientists say it may be five or six years _____ it is possible to test this medicine on human patients.
| A．since | B．after | C．before | D．when |
My brother, ________ is in the army now, used to be an artist.
| A．who | B．that | C．whom | D．which |
________ matters most in learning English is enough practice.
| A．What | B．It | C．That | D．As |
When he woke up, he found ________lying by the sea.
| A．he | B．his | C．him | D．himself |
The chairman thought ________ necessary to invite Professor Smith to speak at the meeting.
| A．this | B．what | C． it |
D．that |
. What ________beautiful day it 
is! Why not go out for _______picnic?
| A．a; / | B．the; a | C．/; a | D．a; a |