The law requires all cars () for safety and efficiency.

单项选择题The weight of something is another way of describing the amount of force exerted on () by gravity.

单项选择题Prior () his departure, he wrote a letter to his mother.

单项选择题The owner of the store promised to give the money back to the traveller（）his return.

A.at
B.from
C.by
D.on

单项选择题Only after I left the place that how ugly and dishonest the people there had been.

单项选择题When the clouds moved in, the moon was no longer () sight.