Man can't live w__________ water or air.
A big smile can bring warmth to people, which ___________ （花费）nothing.
The rainforest will _____________ (消失) one day if humans continue to do harm to the environment.
A____________（世纪）is one hundred years.
Lucy looked through her test paper ________（仔细）in order not to make mistakes.
The new couple like the house very much but they can't ________（负担得起）it.