单选题 The manager is well aware of a few other problems ______ he knows we have had with the customers in the past five years.
A. which
B. those
C. what
D. whichever

【正确答案】 A

【答案解析】超高级问题空格前后有两对“主语+动词”，所以空格内应填入连词。he knows是插入语。B选项不能做连词，what和whichever在前面没有先行词的时候使用。正确答案是which，做关系代词，在从旬中做have had的宾语。
[高频词语] be (well) aware of 充分意识到