以下不是信息源的是（）
A.扫描仪
B.照相机
C.话筒
D.音箱
参考答案：D
It was along the Mississippi River ______ Mark Twain spent much of his childhood _____ the story happened.
A. which; that B. that; which C where; that D. that ;that
小机挂闸后高、低压主汽门打不开怎么办？
