离心泵均采用端面（）密封，往复泵与旋涡泵均采用（）密封。
参考答案：机械；填料
My mother ______ dinner when I got home yesterday. [ ]
A. cooks
B. will cook
C. is cooking
D. was cooking
直肠癌根治性放疗常采用几野照射（）.
A.二野照射
B.三野照射
C.四野照射
D.单野照射
E.五野照射
