下列各组物质，可能（包括一定）互为同系物的是[ ]
A．甲烷和新戊烷
B．CH3Cl和CHCl3
C．C2H2和C2H4
D．C4H8和C9H18
AD
After a long hiking, the boy was ________ tired to walk. [ ]
A. too
B. to
C. so
D. very
在冬季，水环式真空泵停运后需要对泵体进行（）操作。
A.保温
B.充液
C.排液
D.保压
