Hardly A -[I had ] sat down when I B-[heard] C-[someone ] knock at the D-[door] .

你喜欢流行音乐吗?

我们刚才去散步了。

我不能去聚会，因为要准备考试。

不要放弃希望。

我会去火车站接你。

They argue that plastic bottles make up a small portion of the nation ’s total waste.

Corals are particularly sensitive to changes in temperature.

The planet's health depends on the survival of coral reefs.

He was one of the richest and most powerful men of his time.

She was afraid of germs and diseases.