在窗体中添加一个命令按钮，名称为Command1，然后编写如下程序： Private Sub Command1_Click() sum=0 For i=1 To 100 step 2 sum=sum +i Next i MsgBox sum End Sub 窗体打开运行后，单击命令按钮，则消息框的输出结果为______。

America.
B. Mexico.
C. Canada.

A. Take the refrigerator away.
Buy some groceries.
C. Pick out other appliances.

A. how quickly many species of cacti are becoming extinct
B. how quickly much species of cacti is becoming extinct
C. how quickly are many species of cacti becoming extinct
D. how quickly is much species of cacti becoming extinct