两个相似三角形的面积分别为4和9，则这两个三角形的相似比为( )
A：23
B：1681
C：827
D：49
根据对话内容回答问题
A: Hello! Is that Mike?
B: No. This is Tom.
A: Hi, Tom. This is John. How are you?
B: Fine, thanks.
A: Is Mike in?
B: Sorry, he isn't. He's at school.
A: OK. Thank you. Bye—bye!
B: Bye!
