Although there is no life on Mars now , some scientists think that there some form of life a long time ago .
We have the list of items we want, which means that we know ______ what we want.
It is said that sandstorms will become more________ as a result of global warming.
The Sunday of May is Mother’s Day and a time to be _____________ to our mothers.
We have been trying hard to find out the ____________of the homeless man, but without luck, no one can tell who he is.
You can get to Hong Kong using different kinds of ________, by air, by sea or by land.