Correct Option: C

rapid (Adjective) : happening in a short period of time ; done or happening very quickly
gradual (Adjective) : happening slowly over a long period ; not sudden
unscrupulous (Adjective) : without moral principles ; not honest or fair; unprincipled
dynamic (Adjective) : having a lot of energy and a strong personality
enthusiastic (Adjective) : feeling/showing a lot of excitement and interest