According to a UN report, some 844 animals and plants ______ in the last 500 years.
The boss ______ the worker how to do it, or the accident couldn’t have happened.
In the 1930s, the two countries were at ______ war, and his father was fighting at _____ front.
Don't leave for there until__________ to do so.
Tom’s teacher kept on telling him to practise speaking English, but _______ didn’t work.
These plants are watered___________