Li Ming studied very hard. As a result, he succeeded ______ the entrance examination to college.

---Have you finished the report?---Oh, sorry. It was so noisy in the office that I couldn't _______ down to write anything.

When it ______ research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.

He has accepted the job because he likes challenge, and the chance of dealing with difficult problems ____ to him.

 The policeman ______ the traffic to move forward after the traffic light turns green.