Mary is () than her younger sister A a head shorter B taller

选A。Mary is () than her younger sister。Mary 比她妹妹矮（高）一个头。矮（高）一个头 a head shorter/ taller 固定搭配,高矮要用比较级。 再问： 为什么啊 再答： Mary is () than her younger sister。 Mary 比她妹妹矮（高）一个头。 矮（高）一个头 a head shorter/ taller a head放在前，固定搭配，后面有than，高矮要用比较级。