A:3,+∞)
B:(0,3
C:13,+∞)
D:(0,13
729 1086 4003 2408 3124
已知扇形的周长为20,当扇形的圆心角为____ 弧度时,它有最大的面积.
You ______a teacher. I ______ a student. My sister ______a student, too.