成吉思汗的主要功绩是（ ）
A：灭亡西夏
B：统一蒙古
C：建立元朝
D：定都大都
已知x2﹣y2=14，x﹣y=2，则x+y等于（ ）
Next week, ____ the students will have a basketball game.
This book is ____ (interesting) than that one.
