What Particular and Very Important Phenomenon Frequently Occurs in Binary

Multiple Choice

What particular and very important phenomenon frequently occurs in binary star systems where the stars are very close together?

A) The less massive star, in its elliptical orbit, repeatedly passes through the thin, extended atmosphere of the second star, producing periodic rises and falls in light output from the star system.
B) The radiation from the hotter star slowly heats and evaporates away the cooler star.
C) Mass lost from one star is deposited on its companion.
D) The less massive star spirals slowly into its more massive companion because of tidal interactions.