— Why does he never pick up the waste paper on the ground?— Maybe because he thinks it’s beneath his         to do so．

What is the ______ to Beijing and back?

I pity anyone who has to feed a family on such a low ______

Scientists have found no ________of life on Mars so far,though great efforts have made on the research.

Last year the number of studects who graduated with a driving licence reached 200,000, a(n) ________of 40,000 per year.