问题补充：
My grandpa is in his seventies. He’s to take the bus for free.
A. old enough
B. enough old
C. young enough
D. enough young
答案：
(答案→)A. old enough
B. enough old
C. young enough
D. enough young
解析：enough修饰形容词，位于该词之后，又根据第一句内容，可知这位女士是足够大，而可以免费了，故选答案为A
