下列各组物质中,组内两种物质不是同系物的是()
A.硬脂酸甘油酯与三乙酸甘油酯
B.油酸与丙烯酸
C.甘油和十八碳烯酸
D.丙烯酸与软脂酸
参考答案:C, D
______ after a long walk,Tom called and said he couldn't come to the party. [ ]
A. Having worn out
B. Being worn out
C. To be worn out
D. Worn out
了确保123皮带安全运行,设计了以下()开关。
A、跑偏
B、拉绳
C、打滑
D、断煤