用所给单词的适当形式完成短文。

     I made my first trip to clean the forest that afternoon three years ago.I ___1___(take) a big black

rubbish bag with me. Ten minutes after starting to pick up litter, my bag was filled with cans, bottles,

broken glass

and newspapers.

     I ___2___(be) to the forest more than ten times to pick up litter ever since then. I like to be there

and I ___3___(feel) great to do something for the environment.

     I can't understand why people drop litter.  But I ___4___(keep) picking up litter until  they  stop

dropping it.

     What I ___5___(do) now is only a small bit to help the earth, but I still think it is important.    

PVA冷冻机油泵电动机的保护有（）保护。

A、过载

B、短路

C、零序

D、欠压