The machine is hard to （控制）． There must be something wrong with it．
Professor Xu gave us a talk on how to （保护） the environment last week．
The school will hold many activities to （庆祝） our country's 70th birthday．
Shall we go outside and breathe some （新鲜的） air？
Good ideas．
Liu Cixin is the （作家） who wrote the science fiction novel The three Body Problem．