大肠癌最主要的转移途径是 （）
A.血行转移
B.淋巴转移
C.直接蔓延
D.肠腔种植
E.癌细胞脱落
参考答案：B
— Is Tom at school today?
— No, he is at home ______ he has got a bad cold.
A．so
B．or
C．because
D．if
DG-220大钩提环轴销的润滑周期为（）。
A.72h
B.100h
C.168h
D.360h
