天然气体积体积系数的单位是()。
A、米每立方米
B、立方米每米
C、立方米每立方米
D、米每米
参考答案:C
— Where is Tom?
— Look. He _______ in the pool with the boys. [ ]
A. is swim
B. is swimming
C. is swimming
D. swims
人体中由口腔、食道、胃、肠、肝、胰等共同组成的是( )
A.消化腺
B.消化器官
C.消化道
D.消化系统