-- Have you been to the Great Wall?

-- Perhaps not in my memory. _______, it might have been during my early childhood.

A．If any

B．If ever

C．If once

D．If not

在一买卖合同中，甲是买方，乙是卖方。甲乙以下行为中属于双方违约的是（）。

A.甲乙双方约定于同日履行义务，甲带款提货时，因乙没有交货，甲拒绝付款

B.甲乙双方约定甲先付款，乙再交货。甲没有按时付款，乙拒绝到期交货

C.甲乙双方约定甲先付款，乙再交货。甲仅支付部分货款，乙所交货物存在质量缺陷

D.甲乙双方约定甲先付款，乙再交货。甲支付了40％贷款，乙也交付了40％的货物