It came as a great _______ to the parents thattheir son finally came back safe and sound.

What are the young people doing there— They are discussing how to ________ the pollution in the river.

I’m fine — I just felt a bit sleepy and tired, that was ________ I went to bed so early.”

July the 13th,200l _______ a very bright night in Beijing that will never fade from memory．[ ]

I can’t recite the poem. — Well, you are supposed _____ it many times yesterday evening. [ ]