这些代码怎么错了啊

<form name="form1" method="post" action="">
<select name="select1">
<option>——</option>
<option value="c1">1</option>
<option value="c2">2</option>
<option value="c3">3</option>
<option value="c4">4</option>
<option value="c5">5</option>
</select>
<input name="Submit" type="submit" onClick="a()" value="提交">
</form>
<script language="JavaScript" type="text/javascript">
function a() {
if (form1.select1.value = "c1") {
document.write("1")
}
if (form1.select1.value = "c2") {
document.write("2")
}
if (form1.select1.value = "c3") {
document.write("3")<

<form name="form1" method="post" action="">
<select name="select1">
<option>——</option>
<option value="c1">1</option>
<option value="c2">2</option>
<option value="c3">3</option>
<option value="c4">4</option>
<option value="c5">5</option>
</select>
<input name="Submit" type="submit" onClick="a()" value="提交">
</form>
<script language="JavaScript" type="text/javascript">
function a() {
if (form1.select1.value == "c1") {
document.write("1")
}
if (form1.select1.value == "c2") {
document.write("2")
}
if (form1.select1.value == "c3") {
document.write("3")