It never occurred to humans until themid-l990s someanimals can be cloned

Urban crowdedness would be greatly relieved if fares________ on public transport were more reasonable．

According ____ these messages, we knew they were ____ trouble.

Tom _______ up early. But now he gets up very late.

It’s certain that we are ________ to having a clean and beautiful home in the future because some special projects are ________ to protect the environment.