汽轮机的基本工作原理？
参考答案：
蒸汽通过喷嘴时，压力下降，体积膨胀形成高速气流，推动叶轮旋转而作功。
— I haven't seen Tom these days. Where is he?
— He _____ Japan.[ ]
A. has been to
B. has gone to
C. has been in
D. went to
柴油机冒黑烟是何原因？如何排除？
