Every morning Mr. Smith takes a ______ to his office.

Every morning Mr. Smith takes a ______ to his office.
A、20 minutes'walk
B、20 minute's walk
C、20-minutes walk
D、20-minute walk
【正确答案】：D
【题目解析】：数字+连字符+名词单数=所对应的形容词，a 20-minute walk 20分钟的路程。