如果a∥b，b∥c，d⊥a，那么[ ]
A.b⊥d
B.a⊥c
C.b∥d
D.c∥d
答案：A
What does trick or treat mean? It means get a ______ or play a ______. [ ]
A. trick; treat
B. treat; treat
C. trick; trick
D. treat; trick
操作风险可以分为人员因素、内部流程、系统缺陷和外部事件四大类别。（）
