So really this question is asking "which part of this molecule is flat". A normal sp3 carbon with 4 sigma bonds will be tetrahedral. Once we get some pi bonds (formed from either sp2 carbons or sp carbons) we get some "flatness". Thus if you looks at the molecule, how many places are there that can be flat (ie where are there some pi bonds).
Furthermore, the carbons involved in the pi bond are in the same plane. Now here's a hint in case it's not clear...the carbons immediately connected to those carbons in the pi bond are also in the same plane. Once you go out to the second carbon though it's no longer in the same plane (ie carbon 3 is not in the same plane as carbon 5).
Based off of that, what would you answer now?