grammar stuck Q2

[ladyfirsttdbcn]

17. Every magnet has two ends, called north and south poles, where the forces it exert are strongest
Hello again, hjhj, I am getting into stuck with this stuff again, coulda show me where is the wrong one?
IN fact, acoording to the key, the odd one here is " where" but I don't really know why

[CybaSumo]

i dont think there is something wrong in there...

[denvinbo]

17. Every magnet has two ends, called north and south poles, where the forces it exert are strongest
Hello again, hjhj, I am getting into stuck with this stuff again, coulda show me where is the wrong one?
IN fact, acoording to the key, the odd one here is " where" but I don't really know why

There's a small mistake.....that after "it" u have to use "exerts"....not "exert"