we should recycle materials to keep the environment clean.(改

we should recycle materials to keep the environment clean.(改为用it引导的句子)
it is ______ ______ ______ ______ recycle materials,so as to keep the environment clean.
if there were no atmosphere,the earth would be lifeless.(保持原句意思)
______ atmosphere,the earth ______ ______ lifeless.
the boy is so yong that he can't use the computer.(改为简单句)
the boy ______ ______ ______ ______ use the computer.