下列是用来检测某地区酸雨程度的程序，程序调试过程中提示①处出现语法错误，则这一行正确的语句应该为                。
Dim ph As Single, s As String
ph = Val(Text1.Caption)        '①
If ph <=" 4.7" Then
s = "重度酸雨区"
Else
If ph <=" 5.6" Then
s = "轻中度酸雨区"
Else
s = "非酸雨区"
End If
End If
Label2.Caption = s