Mr Stevenson is great to work for-I really couldn’t ask for a ________ boss. [ ]

he waters of this great lake, whichis also the world’s deepest, have been ____ by waste from a chemical factory.

With the living environment becoming worse and worse, many of the earth’s species are ______.

The reason why Malaysia Airline Flight370 disappeared remained_____.

There is something wrong with your bike, ___ -Yes. I’ll have it _ tomorrow.