Suggestions have been put forward guns should be more strictly controlled in the USA.A.

问题补充：

Suggestions have been put forward guns should be more strictly controlled in the USA.

A. before B. that C. when D. as

答案：

解析：考查同位语从句：句意：建议被提出美国的枪支应该被严格控制。同位词是suggestions，that引导同位语从句，对suggestions的内容做出说明，that不做成分，也不能省略。选B。