Ⅰ.用所给词的适当形式填空
1.If the new safety system (put) to use,the accident would never have happened.
答案had been put
2.It was believed that everyone (move) out of the building to safety.
答案had been moved
3.I regretted to tell him that he (dismiss).
答案had been dismissed
4.The report revealed that workers (expose) to high levels of radiation.
答案had been exposed
5.He (trap) for five hours before the help arrived.
答案had been trapped
