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 PrintEnd Sub

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