单项选择题

下面程序运行后,窗体中显示______。
Private Sub Command1_ Click()
a$ = "*": b$ = "$
for k = 1 To 3
x$ = String$(Len(a$) +k, b$)
Print x$;
Next k
Print
End Sub

A.*** ** ***
B.*$*$*$
C.1*$2*$3*$
D.$$$$$$$$$