He has some trouble ______ his classmates, but he has no trouble ______ doing his lessons.
The rare fish,_____ from the cooking pot, has been returned to the sea.
----- I’m taking my driving test tomorrow. ----- _____!
Some insects_____ the colour of their surroundings (环境) to protect themselves.
_____ is known to everybody, the moon travels round the earth once every month.
We are invited to a party _________in our club next Friday.