后面这句that undoubtedly have a good deal of validity 是 定语从句。定grounds。
grounds 理由
。。。has been questioned on grounds that undoubtedly have a good deal of validity.
对。。。。。。。以毫无疑问非常有效的理由提出了质疑
原因状语从句啊 on grounds that 指 原因是
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