function check3choose2()
	{
		var check = 0;
		if(document.form.choice21.checked == true){
			check++;

		}
		if(document.form.choice22.checked == true){
			check++;
		}
		if(document.form.choice23.checked == true){
			check++;
		}
		if(check<2){
			alert("請在頭三項選兩項。");
		}
		else if(check>2){
			alert("頭三項只可以選擇兩項。");
		}
		else {
			document.form.submit();
			}				 
			
	}