问题补充:
The visitors saw rows of houses the roofs are red.
A. where
B. that
C. what
D. of which
答案:
A. where
B. that
C. what
(答案→)D. of which
解析:考查定语从句。本题定语从句的先行词是houses,定语从句中which指代先行词作为of的宾语,the roof of which=whose roof。句意:来访者看到了一排排的房子,这些房子的屋顶都是红色的。故D正确。