有如下VB程序段：

Dim a(1 To 10) As Integer，i As Integer，j As Integer

a(1)=1

a(2)=1

For i=3 To 5

a(i)=1

For j=i-1 To 2 Step -1

a(j)=a(j)+a(j-1)

Next j

Next i

Text1.Text=Str(a(3))

该程序段运行后，在文本框Text1中显示的内容是(  )

A、1

B、3

C、4

D、6