问题补充：
They are talking excitedly about the writers and their books interest them.
A. who
B. whom
C. that
D. Which
答案：
A. who
B. whom
(答案→)C. that
D. Which
解析：此处the writers and their books是先行词，先行词既有人又有物，因此用关系代词that。这里that在定语从句作主语。句意：他们正在激动地谈论使他们感兴趣的作者和他们的书。
