下列式子中正确的是（ ）
A：5+2=7
B：a2−b2=a−b
C：ax−bx=(a−b)x
D：6+82=3+4=3+2
— He thinks that girls are smarter than boys when it comes to learning English.
— But two years ago he thought_______.
给下面的句子选择合适的答语。
①Happy birthday! ____ A. Two books.
②How old are you? ____ B. Thank you.
③How many books? ____ C. You're welcome.
④Let's eat the cake. ____ D. I'm 10.
⑤Thank you. ____ E. Great.
的椭圆Ⅰ与Ⅱ的长半轴的长分别为
和
，半焦距分别为
和
,则下列结论不正确的是 （ ）