凝点测定前，试管中试样经预热和室温下冷却后测定，每观察一次液面（）重新预热、冷却。
A.必须
B.不必要
C.二者均可
参考答案：A
读短文做练习。
My family will go on a trip to Beijing. I invite my best friend Jenny. She lives in Ottawa. Ottawa is far from
Shijiazhuang. Jenny wants to come to Shijiazhuang by plane. She will stay with us for two days. Then we are
going to Beijing by train.
1. Who will go to Beijing?
A. My mother
B. My father
C. My family
2. Where does Jenny live? .
A. Beijing.
B. Shijiazhuang.
C. Ottawa.
3. How does Jenny go to Shijiazhuang?
A. By plane.
B. By train.
C. By bus.
4. How do we go to Beijing?
魏延造反结果死于何人手上？
