Yes, simply set the option "Yes" to selected.
<option value="Y" selected>
Or another possibility
Code:
function toggleRows(select, rows) {
var si = select.selectedIndex;
if (si == 0) {si = 1}
var display = si == 1 ? '' : 'none';
Quizmaster: In Roman Catholicism, baptism, confirmation and matrimony are three of the seven what?
Contestant: Deadly sins.