单项选择题

有如下程序:
Private Sub Command1_Click( )
a$="A WORKER IS OVER THERE"
x=Len(a $)
For i=1 To x-1
b$=Mid $(a $,i,2)
If b $="ER"Then s=s+1
Next i
Pdnt s
End Sub
程序运行后的输出结果是

A.1
B.2
C.3
D.4