选出每组单词中画线部分的发音不同于其他三个不同的选项
A answer B black Ccalculator 画线：a
A her B sister Cshirt 划线：A er B er Cirt
Awhere B which Cwhose 划线：wh
A comb B come Cover 划线：o
A room B cool C cook 画线;oo