Error while passing dropdown value to the function

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C#

C#4.0

How to Pass value of dropdown to the function as paramete

my code is

protected void PayWithPayPal(string amount, string itemInfo, string name,
         string phone, string email, string currency)

and i am passsing value like this

protected void btnPay_AsPerYourChoice(object sender, EventArgs e)
   {
       PayWithPayPal(txtAmount,txtPurpose,txtName,txtPhone,txtEmailId,ToString().(ddlCurrency.SelectedItem));
   }

Dropdown code is

<asp:DropDownList runat="server" ID="ddlCurrency" Style="margin-left: 42px;
        width: 204px; background-image: transparent url('../images/txtBoxbg.jpg') no-repeat;">
        <asp:ListItem>- Select -</asp:ListItem>
        <asp:ListItem>INR</asp:ListItem>
        <asp:ListItem>USD</asp:ListItem>
        <asp:ListItem>EURO</asp:ListItem>
        <asp:ListItem>Pound</asp:ListItem>
    </asp:DropDownList>

Getting error
:Identifier Required