测井下井仪器的密封，由（）来承担。
A.丝扣
B.顶丝
C.“O”圈
D.丝扣油
参考答案：C
—Would she mind playing against her former teammates?
—________ She is willing to play against any tough players.[ ]
A. I think so.
B. I'm not surprised.
C. Of course.
D. Not likely!
某气体的分子组成是RO2，在标准状况下，1．28 g这种气体的体积是448 mL。求此气体的摩尔质量和R的相对原子质量。
