At the railway station,the mother waved goodbye to her daughter until the train was________.
32._____from lightweight materials,the robots are about the size of a human arm or smaller.
31.The fact that smoking is harmful to health is____most smokers are quite aware of.
30.It was_________ back home after the experiment.
29.An example of them is fraud, a crime _______ money is stolen by cheating others.
28. Dr. Frank failed many times but he finally _____ to find a successful way to solve the problem.