定语从句一道选择12.Read the text a second time and you will probably

c
此句可断为
Read the text a second time and you will probably know what the principle is/ on which a hovercraft works.
hovercraft是在principle的基础上运转的
也就是说,如果你不看前面也行
也就是
you will probably know what the principle is
和
on which a hovercraft works.
这两句
而which 是指principle
第二句就等于是hovercraft works on the principle
明白了么?
要不我翻译一下；再把这篇文章看一遍,你或许会知道使喷气助推器工作的这个原理是什么