分享验证码和提交按钮

Question

我无法解决验证码一整周的问题。我在谷歌找到了简单的数学验证码，现在我需要结合两个按钮：检查（验证码）和一个按钮发送按钮。现在，当我尝试在验证码上正确答案后发送信件时，我看到失败错误。任何建议都会受到很大关注！

<script type="text/javascript">
    var a = Math.ceil(Math.random() * 10);
    var b = Math.ceil(Math.random() * 10);       
    var c = a + b
    function DrawBotBoot()
    {
        document.write("What is "+ a + " + " + b +"? ");
        document.write("<input id='BotBootInput' type='text' maxlength='2' size='2'/>");
    }    
    function ValidBotBoot(){
        var d = document.getElementById('BotBootInput').value;
        if (d == c) return window.open('','_top');        
        return alert(false);
    }
    </script>
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