为什么点击按钮“女”，出现的内容依旧是“男性”？

Question

<input type="button" id="man"  value="男" onclick="show()" checked="checked" ><input type="button" id="woman" value="女" onclick="show()" checked="checked"><p style="display:none" id="div1">男性</p><p style="display:none" id="div2">女性</p></body><script type="text/javascript">function show(){if(document.getElementById("man").checked){ document.getElementById("div1").style.display="block"; document.getElementById("div2").style.display="none"; }else if(document.getElementById("woman").checked){ document.getElementById("div2").style.display="block"; document.getElementById("div1").style.display="none"; } }</script>