He managed to make himself ___ in his ___ English.

After the big earthquake，his house was completely ______，so he had to build a new one ______ the old house stood.

Scientists _______ a lot of experiments on animals, hoping to find and effective way to cure the patients who had AIDS.

Think twice before you         others’ cheating in the exam, because you are not going to help but indeed to kill their motivation for study.

We should protect the environment, for plenty of fresh air ________ to good health.