题干
—Where’s your mother ?
--She has gone shopping with my aunt . She’ll be back ________.
--She has gone shopping with my aunt . She’ll be back ________.
A：in a while
B：for a which
C：once in a while
D：a while
答案(点此获取答案解析）
A
， 
，π， 
，cos45°， 
中是无理数的个数有（ ）个．