Only when the European countries' financial system broke down _____to take measures to deal with those problems．

A．did they decide

B．they decided

C．they had decided

D．had they decided

商务中的惯常做法和各种价格条件要构成一项国际贸易惯例，应具备下列哪些条件（）。

A.是国际贸易中长期、普遍的作法

B.有确定的规则或内容

C.由有关国家法律加以认可

D.有强制适用的效力