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