Answer:
The most effective way to combine sentences (3) and (4) is "In the story, a man is haunted by an old man’s eye, which he thinks looks like the eye of a vulture."
Step-by-step explanation:
The best way to connect sentences three and four is to have them as one dependant sentence and an independent one that is connected by a relative pronoun, this makes the sentences four an extension of sentence three adding information by specifying details about the old man's eye that is mentioned in line three.