Final answer:
The correct answer is option a) He is too ill to leave his room.
Step-by-step explanation:
The reason Isabella says Hindley can't attend Catherine's funeral in Chapter 17 is not explicitly mentioned in the text that you provided. The question seems to be related to the novel 'Wuthering Heights' by Emily Brontë. In the context of that novel, the answer to why Hindley could not attend Catherine's funeral would be a) He is too ill to leave his room.
Hindley's decline is well documented throughout the novel, showing him falling into a state of despair and various addictions after the death of his wife. By the time of Catherine's death, Hindley is in such a poor state that attending her funeral would not have been possible for him.