________ the problem of land erosion(侵蚀) getting more serious, the government is searching for a way to deal with it.
He is always serious and doesn’t like _____.
No one knows when such a custom first _____.
The students pretended_______ attentively when the teacher came in.
________ he returns to his native land.
--- Hi, Torry, can I use your computer for a while this afternoon? --- Sorry, _____________.