His knowledge of genetic engineering earned him a ______ as an expert in the field.

Once environmental damage __________ , it takes many years for the system to recover.

_________ with the size of the whole earth, the highest mountain does not seem high at all.

The news ____________ he had landed on the moon spread all over the world.

Only after I had reached the airport ________ that I had forgotten to take my ticket with me.

It suddenly occurred to me that we could ________ the police for help.

He has been away from home ________ three months ago.

News came from the sales manager ________ the new product had been selling well in the local market for three months.

It is required that anyone applying for a driver＇s license____a set of tests.

The ratio of the work done by the machine __________ the work done on it is called the efficiency of the machine.

We were depressed ____________ the bad news.