补充句子
The robbers hit them ________. They couldn’t bear it any more so they decided to answer ________ with ________ and began their ________ fightback.(violent)
This object gives off ________ gases. They may do ________ to our health. You must make the object ________ before you use it.(harmful)
Do you believe in the ________ of ghosts? Perhaps they only ________ in the minds of some people.(exist)