螺杆泵螺杆卡住的原因是（）
A、螺杆与泵体间隙大
B、介质粘度大
C、螺杆与传动杆销断
D、介质含颗粒
参考答案：D
用括号内单词的适当形式填空完成句子。
1. Yesterday they _ _ (have) an English lunch.
2. She says English food (be) delicious.
3. What did you _ (have) last night?
4. She had a bowl of _ (noodle).
5. Did you have (sandwich)?
某班有男生24人，女生21人，现在要从中选1名学生当领操员，选中的这名学生是男生的概率是﹙ ﹚．
