炉前使用煤气时应先点火后开煤气。
参考答案：对
若|x|=3，则|x|﹣x= [ ]
A．0
B．0或3
C．3或6
D．0或6
Li Lei likes English very much, and she does her best ______ English well. [ ]
A. to learn
B. learn
C. learning
