题干
The boy is ____. Today is his ____birthday.
A：twelfth, twelfth
B：twelve, twelve
C：twelve, twelfth
D：twelfth, twelve
答案(点此获取答案解析）
C
The boy is ____. Today is his ____birthday.
A：twelfth, twelfth
B：twelve, twelve
C：twelve, twelfth
D：twelfth, twelve
a、y1、y2、b成等比数列，那么
等于（ ）