How to disable another dropdown list when text is select in a dropdownlist?

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C#

As select is for customers to select values, I want the second dropdown list to be unclickable

What I have tried:

DdlTerm.Enabled = false;
DdlTerm.Items.Clear();



if (DDlLoanType.Text != "Select")
{

string query = string.Format("select LoanTerm, LoanRate from LoanRates where LoanType = '" + DDlLoanType.Text + "'");
BindDropDownList(DdlTerm, query, "LoanTerm", "LoanRate", "Select");
DdlTerm.Enabled = true;
}
else
{

DdlTerm.Enabled = false;
DdlTerm.Items.Clear();
}