With a lot of difficult problems ________, the manager felt worried all the time.
A:settled
B:to be settled
C:settling
D:to settle
纤维长度
(0,100)
100,200)
200,300)
300,400)
400,500
甲地(根数)
3
4
5
乙地(根数)
1
2
10
6
“中东”通常是指( )