关于一句英语句子的疑惑："The main reason is ____that+从句",空内是填obvious还是obvious_英语解答

关于一句英语句子的疑惑："The main reason is ____that+从句",空内是填obvious还是obviously?
答案就是从obvious和obviously里面选择,并给下原因,

人气：190 ℃　时间：2020-06-04 05:11:43

解答

The main reason is obviously that
显而易见,这最主要的原因是你的答案应该是对的，能给解释一下么？为什么obvious不可以，它作表语难道不对么？