A. For the first time
B. The first time
C. It was the first time
D. First of all
例六No sooner had the clerk arrived office _____ he started his computer.
A. than B. but
C. when D. then
例七 _____environmental damage is done, it takes many years for the ecosystem to recover.
A. Even if
B. If only
C. While
D. Once
答案：DAADBAD
②表示原因： because, as, since, now that，considering that, seeing that等。
例一 Parents should take seriously their children’s requests for sunglasses _____ eye protection is necessary in sunny weather.
A. because B. though
C. unless D. if
例二Jenny was very sad over the loss of the photos she had shot at Canada, ____this was a memory she especially treasured.
A. as B. if
C. when D. where
答案：AA
③表示条件： if, unless，so long as, in case（万一)，on condition that, only if，providing/provided that, suppose/supposing that(倘若假使) 等。
例一In time of serious accidents, ___we know some basic things about first aid, we can save lives.
A. whether B. until
C. if D. unless
例二 We won’t keep winning games _____we keep playing well.
A. because B. unless
C. when D. while
例三 Leave your key with a neighbor ___ you lock yourself out one day
A. ever since B. even if
C. soon after D. in case
例四 —— What are you going to do this afternoon?
—— I’ll probably go for a walk later on it stays fine．
A．as far as B．so long as
C．even if D．as if
例五 John's mother allowed him to go swimming ___that he didn't go too far from the bank.
A. if B. unless
