The correct answer is C. Vindictive.
A vindictive person is one who is determined to exact full vengeance for wrongs done to him. They are often angry and resentful, and they may seek to harm or punish the person who has wronged them.
A vindicator is someone who seeks to avenge a wrong. They may be motivated by a sense of justice or by a desire to protect others from harm.
A usurer is someone who lends money at high interest rates. They are often seen as greedy and exploitative.
A virulent person is someone who is very sick or who has a very strong feeling of hatred or anger.
In this case, the correct answer is C. Vindictive. The question is asking for someone who is determined to exact full vengeance for wrongs done to him. This is a definition of vindictiveness. The other options do not match this definition.