12.Read the text a second time and you will probably know what the principle ______ a hovercraft works.A.is on thatB.has on whichC.is on whichD.on which
问题描述：
12.Read the text a second time and you will probably know what the principle ______ a hovercraft works.
A.is on that
B.has on which
C.is on which
D.on which
答