A - a brown dwarf
Since degeneracy pressure is what stops the collapse of white dwarfs (electron degeneracy) and neutron stars (neutron degeneracy), the exceptions would be A, D, and E, wouldn't they?
If you include metallic hydrogen as degenerate matter, then D and E are not exceptions either.
The best answer is A because brown dwarfs do not have enough mass to initiate fusion, let alone produce degenerate matter in any form. Thus, normal gas pressure stops the collapse of a brown dwarf.