sql语句错误

根据年级选择表执行查询，查询条件的两个字段是或的关系

Private Sub 年级_AfterUpdate()
Me.模块.Requery
Me.模块 = ""
Mynew
End Sub

Private Sub 模块_AfterUpdate()
Mynew
End Sub
Private Sub B类模块_AfterUpdate()
My2new
End Sub
Sub Mynew()

sheet = " & Me.年级 & "

str = " where true "
If Nz(Me.年级) <> "" Then
    str = str & " and " & "GradeName ='" & Me.年级 & "'"
End If

If Nz(Me.模块) <> "" Then
    str = str & " and " & "ModularName ='" & Me.模块 & "'"
End If

Me.窗体1.Form.RecordSource = "select A_类模块, A_ModularContents, Choice, from '" & sheet & "' &'" & str
End Sub
Sub My2new()
sheet = " & Me.年级 & "
str = " where true "
If Nz(Me.年级) <> "" Then
    str = str & " and " & "GradeName ='" & Me.年级 & "'"
End If

If Nz(Me.B类模块) <> "" Then
    str = str & " and " & "ModularName ='" & Me.B类模块 & "'"
End If

Me.窗体1.Form.RecordSource = "select B_类模块, B_ModularContents, Choice,time from '" & sheet & "' &'" & str

End Sub