阅读理解
Jenny is Mr. White's little daughter. She is good at Art . But she isn't good at Math. Mr. White is teaching her ,”What's six plus three?”
Jenny counts her fingers and answers ,”It's nine .”
“Good .What's twenty minus three?”
Anna counts her fingers and toes. “Mm.it's five .No , it's seventeen .”Jenny answers slowly.
“What's eleven plus twelve, then ?”Jenny looks at her fingers and toes . They are not enough (足够). Seeing this , Mr. White isn't glad and says, “Use your head, Jenny .”
“That's not enough .I've got only one head.”
根据短文内容，判断下列句子是否正确。
中，自变量x的取值范围是( )
、带电量为
的小球从圆弧管的水平直径端点A由静止释放，小球沿细管滑到最低点B时，对管壁恰好无压力，则圆心处电荷在B点处的电场强度的大小为（ ）