问题补充:
The old town has narrow streets and small houses are built close to each other.
A. they
B. where
C. what
D. that
答案:
A. they
B. where
C. what
(答案→)D. that
解析:考查定语从句。That are built close to each other修饰先行词narrow streets and small houses. That在句中做主语。