I soon found that the work I was doing had already been done, _____, I was wasting my time.

Those who continuously acquire new knowledge that they can ______ their work are more likely to succeed. 

Science and technology __________ nowadays in our socialist construction.

He does help others, but he always expects returns ____. As a result, nobody will accept anything from him. 

Mary wanted to travel around the world all by herself, but her parents did not _______ her to do so.