燃气管道绝热层要具有一定的强度，一般应能承受（）MPa的压力。
A、0.1
B、0.3
C、0.5
D、0.7
参考答案：B
I _________ it everywhere, but I didn't _________ it. [ ]
A. looked for; looked for
B. looked for; find
C. found; looked for
D. find; look for
在图所示四个实验中能用来探究电磁感应现象的是 [ ]
A.
B.
C.
D.
