To be a scientist, you are supposed to have a creative b________.
To his parents' great s____________, Robert got good grades in the final exam.
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.
