All the students in miss osbourne's class like pizza. jeff is a student who likes pizza. therefore, jeff is a student in miss osbourne's class. true, falls, uncertain?

False.  That set of statements forms a syllogism
with an undistributed middle.

It's nice that all the students in Miss Osbourne's class like pizza.
You can be sure that if you meet a student from Miss Osbourne's
class, you've met a student who likes pizza.

But they are not an exclusive club.  They are not the only students
in the world who like pizza.  There are other people in the world who
also like pizza.  When you meet a student who likes pizza, he may be
one of those others.  He may never have even heard of Miss Osbourne.