答：1. A What is your shoe size ?
析：名词作宾语,一般用单数,即使是平时成双出现的如shoe,例: two shoe makers. 两个鞋匠.
例外：man, woman作定语时： a man doctor. two men doctors
2. B. What size are your shoes?
析：your shoes指你的这双鞋子,是复数概念.谓语用are,
3. What is the size of your shoes?
析：正常人都是一双鞋,复数.用单数则有可能暗示对方是只有一只脚的残疾人.