It’s an agreement between towns or cities, _______ have similar features, such as industry, culture and entertainment.

Tom read this poem; his voice was quiet but every word was ______.[ ]

Not easy as the problem of pollution is ____, no one should just stop trying.[ ]

We’re heard much _______ about the missing plane, but we still don’t know where it is.

I felt when I heard Li Kaifu was ill. —But I didn’t. You know, he always worked too hard and didn’t sleep enough.