The little boy has proved his cleverness in the television quiz．

The children were picking tomatoes in the garden．

Only the best players were picked to play in the game．

The Chinese People’s Liberation Army defends our motherland．

Every young man is responsible to serve in the army．

Once seen, it can never be forgotten．

Once water begins to boil, its temperature no longer rises．

Once you begin you must continue．

Scientific theories must be based on facts．

That pilot travels all over the world but London is his base．