True or false? B cells were originally isolated from the bursa in chickens

True

Explanation:

B cells are B lymphocytes and are one of the types of white blood cells. Their main role is in the acquired immune system in which they help in the humoral immune response of the body by the secretion of antibodies. The maturation of the B cells occurs in the bone marrow in mammals. But in birds, these cells mature in an organ named bursa of Fabricius which is a lymphoid organ in birds. These B cells were first isolated form the bursa of Fabricius of the birds.

Many theories can never be proven. 
Here are a few examples:

-- The moon orbits the Earth.
-- Gravity pulls all masses toward each other.
-- The Earth orbits the sun.
-- Everything is made of atoms and molecules.
-- Atoms are made of protons, neutrons, and electrons.
-- Electrons moving through a wire make electric current.
-- The center of the Earth is molten iron and nickel.
-- The source of the sun's energy is nuclear fusion in its core.
-- Almost all galaxies are moving away from us.
-- The universe is expanding.

None of these statements can be proven.  That's why they're not called
Facts or Laws. 

It also tells you that some pretty powerful stuff has been done with concepts
that can't be proven.  If you want to make an idea look foolish, that doesn't
happen when you say "it's only a theory".