A player of a video game is confronted with a series of four opponents and an 80% probability of defeating each opponent. Assume that the results from opponents are independent (and that when the player is defeated by an opponent the game ends).

a. What is the probability that a player defeats all four opponents in a game?

b. What is the probability that a player defeats at least two opponents in a game?

c. If the game is played three times, what is the probability that the player defeats all four opponents at least once?