几个英语完型填空的疑点1、Is it safe to do skydiving?Yes,____ we receive

几个英语完型填空的疑点
1、Is it safe to do skydiving?Yes,____ we receive proper training.
A.as long as B.as well as C.if D.unless
正确打案为什么是A?C不对么?
2、If you leave something important on a bus or underground train while traveling around London,you should _____ the London Trasport Lost Property.
A.look at B.visit C.see D.watch
正确答案为什么是A?B不对么?
3、Telephone plays an important part in daily life.You can____ what is happening on the other side of the world by telephone.
A.see B.make C.hear D.learn
正确答案为什么是D?C不对么?
4、He came from far behind to win.
这句如何翻译?
5、These first "dogs" were not like____we have now.
A.where B.what C.when D.which
选什么?为什么?