The meaning of the given words are:
Sloth means slow or lazy.
Indolence also means reluctance to work and is a synonym for sloth.
Approval means agreeing to something or permission for something.
Enthusiasm means eagerness for something.
"Alacrity" means readiness or willingness. Based on the meanings, the only option that means the same as "alacrity" is "enthusiasm." So, the correct answer is option C.