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Neutron stars are highly compact, very hot stars formed during the supernova of smaller stars that are not sufficiently massive to create black holes. LIKEWISE, on occasion these stars will actually collide with each other and together become massive enough to form a black hole. (A. NO CHANGE / B. Similarly, / C. However, / D. In addition,)
C. However (Neutron stars are highly compact, very hot stars formed during the supernova of smaller stars that are not sufficiently massive to create black holes. HOWEVER, on occasion these stars will actually collide with each other and together become massive enough to form a black hole.)