The correct answer is: A. generous
A miser is a person who is extremely unwilling to spend money or give away possessions. A generous person is the opposite: they are willing to give away money or possessions freely.
B. Liberal is an adjective that can mean “generous” or “open-minded.” However, it can also mean “having or relating to political or social views that are tolerant of or respectful of different ideas or lifestyles.” In this context, “liberal” is not the opposite of “miserly.”
C. Avaricious is an adjective that means “greedy for wealth or possessions.” This is very similar to “miserly,” so it is not the opposite of “miserly.”
D. Charitable is an adjective that means “generous in giving to others.” This is the opposite of “miserly.”