已知x+y=6，xy=4，x2+y2=______．
∵x+y=6，xy=4，
∴x2+y2=（x+y）2-2xy=36-8=28．
故本题答案为：28．
在组织承诺中，员工为了不失去多年投入所换来的待遇而不得不继续留在该组织内的承诺是（）。
A.继续承诺
B.情感承诺
C.规范承诺
D.职业承诺
Great changes in my hometown these years. [ ]
A. took place
B. take place
C. have taken place
D. were taken place
