In my opinion, it’s the best use that could be ______ this machine.
16. After he left college, he was employed in an international company and _______ there ever since.
15. The factory _______ large numbers of tractors to the peasants.
14. The teacher insisted _______ until we finished the work.
13. — How do you keep fit? — By having a healthy diet and _________ regularly.
12. Having finished their morning work, the clerks stood up behind their desks, ________ themselves.