The old town has narrow streets and small houses are built close to each other. A. they B

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：句中先行词为small houses，在定语从句中作主语，故用关系代词that。句意：老镇有狭窄的街道，小房子建得彼此相靠近。