Answer:
Powerful
Step-by-step explanation:
Influential means to hold the power to persuade.
Unmoving cannot be true because it does not mean anything regarding the amount of influence one has.
Useful is not true because being influential can be useful but useful does not have the same meaning as being influential.
Sick mean to be struck with an illness which has nothing to do with how influential one is
Powerful is the best option because someone who is very powerful could also be described as very influential