灵活就业人员是指以（）从业的人员。
A、稳定形式
B、灵活形式
C、全日制形式
D、固定形式
参考答案：B
He had a wide ____ of interests, which made him a popular person that all of us like to make friends with. [ ]
A. world
B. variety
C. various
D. difference
已知数列{an}为等差数列，Sn为其前n项和且a6-a4=4，a11=21，Sk=9，则k=______．
