In order to keep the balance of ecosystem, every possible means _______to deal with the problems of the over-exploiting of natural resources

Like some of my classmates,I can’t live up to my teachers’ expectations., I let them down[ ]

The letter he had been looking forward to________at last this morning.[ ]

Not until he retired from teaching three years ago _______having a holiday abroad .

I haven’t been to Shanghai for years.—You really need to pay a visit, and you’ll find changes there are imagination (想象).