Although the term "psychopath" is popularly applied to an especially brutal criminal, in psychology it is someone who is apparently incapable of feeling compassion or the pangs of conscience.
(A) it is someone who is
(B) it is a person
(C) they are people who are
(D) it refers to someone who is
(E) it is in reference to people
题目分析：首先用they就不对，因为指代的是一个单数的psychopath，用refer表达的是“指的是”这个意思，比用be动词意思更为准确，refer显然比in reference表达方式更为高效一些！
