The old town has narrow streets and small houses are built close to each other.
A. they
B. where
C. what
D. that
网友回答
A. they
B. where
C. what
(答案→)D. that
解析：考查定语从句：先行词是narrow streets and small houses，定语从句缺乏主语，定语从句用that引导，句意：这个古镇有狭窄的街道和小房子，彼此建的很近。选D。