单击命令按钮时，下列程序段的执行结果为()。privAtE suBCommAnD1_CliCk() Dim FirststrAs stringFirststr="ABCDEF"print piCkmiD(Firststr) EnD suBprivAtE FunCtion piCkmiD(xstrAs string)As string Dim tEmpstrAs string,strlEnAs intEgErtEmpstr=" "strlEn=lEn(xstr)i=1 Do whilE i＜=strlEn/2tEmpstr=tEmpstr+miD(xstr,i,1)+miD(xstr,strlEn-i+1,1)i=i+1looppiCkmiD=tEmpstr EnD FunCFion
A、ABCDEF
B．FED
C．FEDCBA
D、DEFABC