________ these experiments were successfully completed would we think of going into humans.

When we ______ the railway station, the train _____ for 5 minutes. [ ]

In order to ______ a good knowledge of English, he gave up his job and went to study in an English school.[ ]

The digital camera is so great. I’ve never seen a better one before, but the price of it is______ in the store.

It was only when I read this story for a second time _____ to appreciate its beauty. [ ]