Some problems in the lecture by Mr.Smith are very popular in our school such as the wast

问题补充：

Some problems in the lecture by Mr.Smith are very popular in our school, such as the waste of electricity, water and food, etc...

A. referring

B. referred to

C. referring to

D. were referred

答案：

A. referring

(答案→)B. referred to

C. referring to

D. were referred

解析：考察非谓语动词。句意：在讲座上被史密斯先生涉及到的一些问题带我们学校非常普遍……，过去分词作定语表示被动的，发生过的动作，problem是涉及的对象，故选B。