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<!DOCTYPE html> <html> <head> <script> function changeSize() { document.getElementById("mySelect").size = 4; } </script> </head> <body> <form> <select id="mySelect"> <option>Apple</option> <option>Banana</option> <option>Orange</option> <option>Melon</option> </select> <input type="button" onclick="changeSize()" value="Change size"> </form> </body> </html>