润滑油中的过滤网应定期进行清洗或更换，防止（）而使润滑油压下降。
A.滤网损坏
B.滤网破口
C.滤网堵塞
D.滤网无法切换
参考答案：C
根据课文内容填空。
It's 1.____ afternoon. The students are 2.____ 3.____ their 4.____. Wang Bing usually surfs 5.____ 6.____, goes 7.____ and plays 8.____ at the 9.____. Mike often goes 10.____, 1istens to 11.____ or 12.____. Helen likes 13.____ 14.____ at home. Yang Ling often does 15.____ at the weekends. Su Hai and Su Yang often 16.____ 17.____ and sometimes they 18.____ 19.____ in the park.
胰腺损伤在各种腹部损伤中所占比例为
A．1%～2%
B．5%～10%
C．16%～20%
D．25%～35%
E．40%～50%
