Many scientists have believed that there may be a _________of life on the Mar．

Ancient Greeks were responsible for many of the _______ in science and other fields.

Most graduates in big cities are suffering form       connected to soaring house prices and job hunting.

—I have to ask a(n) _____ of you because the luggage is too heavy for me.—Oh, with pleasure.

 The storm sweeping over this area now is sure to cause _____ of vegetables in the coming days.