By no means true that all native speakers of English know their own language very well．
A. is that
B. that is
C. is it
D. it is
网友回答
A. is that
B. that is
(答案→)C. is it
D. it is
解析：考查倒装句。By no means 意为绝不，否定词放句首时，要用部分倒装，排除BD.根据句子结构可知，该句为主语从句，it 作形式主语。
句意为每个以英语为母语的人都很好地了解他们都语言，这绝不是真的。