能够燃烧的低压液化气体共有（）种。
A.5
B.6
C.17
D.25
参考答案：D
膨胀水罐和膨胀管的功能是补偿贮热设备及管网中水温升高后水体积的膨胀，以防止（）。
A.系统超载
B.系统超压
C.系统超高
D.系统减压
—What can you see in the picture?
—I can see a farm. And there _____ a lot of animals on it. [ ]
A. is
B. are
C. be
D. am
