______ it have been the failure to pick up directions from the ground control that caused the air crash?
_______, we continued our way.
________ in Tibet for ten years, he has been accustomed to the life and the climate there.
Look! What a mess the room is! In my opinion, it needs ______.
--- Don’t waste any paper, because our forests ____ every day. ----Sorry, I didn’t know that.
The child, who has a gift for sports, might make a first-class tennis player if given chances to develop her ______.