根据问句,单选合适的答句。(将合适的序号填在横线上)
A. How nice. B. OK. Let's go. C. Not so good. D. OK. Good night. E. Good morning.
① x−25=34
② x+23=2
③ x−2.4=35
④ 3x−2.4=x
⑤ 715+x=23
⑥ x−(13+12)=38
This isn't your book,______?