Dim sheet As Excel.Worksheet = worksheets.Item(一)出错。

Dim sheet As Excel.Worksheet = worksheets.Item(1)出错。。
全部代码如下  
Dim   app   As   New   Excel.Application
Dim   workbooks   As   Excel.Workbooks
Dim   workbook   As   Excel._Workbook   =   workbooks.Add(XlWBATemplate.xlWBATWorksheet)
Dim   worksheets   As   Excel.Sheets   =   workbook.Worksheets
Dim   sheet   As   Excel.Worksheet   =   worksheets.Item(1)

最后一句提示：   Option   Strict   On   不允许从“System.Object”到“Excel.Worksheet”的隐式转换。
什么原因啊？


[解决办法]
Dim sheet As Excel.Worksheet = worksheets.Item(1)
改为
Dim sheet As Excel.Worksheet = worksheets.Sheets(1)