关于阴茎海绵体造影检查诊断ED，叙述正确的有（）

A.可用于诊断动脉性ED和静脉性ED

B.阴茎背深静脉显影表示静脉性ED

C.背静脉和前列腺周静脉丛显影或背浅静脉显影表示静脉性ED

D.阴部内外静脉系统显影表示静脉性ED

E.阴茎浅静脉显影表示静脉性ED

An analyst does research about trade restriction. A primary reason for a country to adopt restrictions on international trade is that restrictions typically:

A. improve short-run economic efficiency.
B. benefit consumers at the expense of producers.
C. provide concentrated benefits to a small group of people.