（2018·天津）Kae, _________sister I shared a room with when we were at college, has gone to work in Australia.
A. whom B. that
C. whose D. her
（2018·北京）She and her family bicycle to work, _________ helps them keep fit.
A. which B. who
C. as D. that
（2018·江苏）Self-driving is an area _______ China and the rest of the world are on the same starting line.
A. that B. where
C. which D. when
Ever since he left school, he ______ becoming a professor in that famous university.
A. has never dreamed of B. had never dreamed of
C. didn’t dream of D. was not dreaming of
This machine is very easy ________ . Anybody can learn to use it in a few minutes.
A. operating(操作) B. to be operating
C. operated D. to operate
The game is not very difficult _______ you understand the rules.
A. until B. though
C. once D. unless
