Scientists say it may be five or ten years________ it is possible to test this medicine on human patients.[ ]

I _______ by his story that he made up.

y is apublic holiday, ___ children should get close to nature －But most ofthem have several lessons to attend

.．When Icame into the classroom , I found him _______ with his study.

carbon lifestyle is of great benefit toimprove the world environment can be enjoyed from it until you have a deep understanding of it,however