(加试题) 有程序段
n = 0: i = 1
Do While i <= 4
y = False
For j = 5 To i + 1 Step -1
If a(j) > a(i) Then
y = True
n = n + 1
t = a(j): a(j) = a(i): a(i) = t
End If
Next i
If y = False Then Exit Do
i = i + 1
Loop
数组元素a(1)到a(5)的值依次为“43，18，5，26，51”，经过该程序加工后，变量n的值为( )

A．5

B．4

C．3

D．2