Answer:
I think the answer would be B.
Step-by-step explanation:
Try to plug each sentence in to ameliorate, because that is what I do.
In Frankenstein, the stranger is told that they would like to make his fears more colorful.
In Frankenstein, the stranger is told that they would like to make his fears better.
In Frankenstein, the stranger is told that they would like to make his fears increase.
In Frankenstein, the stranger is told that they would like to make his fears strengthen.
I think the second sentence sounds the best.