有个英语句子的结构我看不懂，求大神分析

Question

their significance may have remained clear had the chinese not come under foreign influence.
请高手指导下这个句子的结构，尤其是这个had 在这里我完全看不懂

Answer 1

这是个含有倒装的虚拟语气结构，had the Chinese not come under foreign influence.
相当于 If the Chinese had not come under foreign influence

从句的意思是“如果不是受到外来影响的话，它们的重要性可能会更清楚些，。。。”
但事实上已经受到了这种外来影响，重要性可能会更清楚些就不那么清楚了。

Answer 2

这是一句对过去事实假设的虚拟语气句子结构。把had提前面可以省略if，引起部分倒装句。
还原后：Their significance may have remained clear if the chinese had not come under foreign influence.
可以查阅语法书中“虚拟语气”与“倒装句”栏目。

Answer 3

正常语序应该是their significance may have remained clear that the chinese had not come under foreign influence.
他在这里把had提前了。

Answer 4

其意义可能仍然不明确的有中国受外国影响的到来。