---Each of the students working hard at their lessons ________ the book. ---- So have I.

When the old man ______ to walk back to his house, the sun       itself behind the mountain. 

Every few years, the coal workers ___________ their lungs X-rayed to ensure their health.

A kind of newly­made shoes, if put into the market, ________ large orders because the heels can switch from 9 to 4 centimeters.

 If their marketing plans succeed，they ________ their sales by 20 percent.