According to the Bronsted-Lowry definition,

an acid is a proton acceptor

a base is a proton donor

a base produces H+ ions in aqueous solutions

a base is a proton acceptor

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium