—Listen! Is Mary singing in the next room?—No. It _______ be Mary．She has gone to Shanghai for an important meeting.

－What do you think we can do for our aged parents?－You_______ do anything except to be with them and be yourself.

It doesn’t often snow in my hometown in winter, but it ___be rather cold sometimes. 

My book, The House of Hales, is missing. Who ________ have taken it?

When we were in the college, we       stay in the library, devoting ourselves to books.