氧探头是测量炉内气氛（）的检测元件。
A.氧含量
B.一氧化碳
C.二氧化碳
参考答案：A
The old woman has a son and two daughters, and are college students now.
A．all of whom
B．both of whom
C．all of them
D．both of them
A我B一名普通教师，C说不上D有多大的学问。
A．只是
B．只是
C．只是
D．只是
