Final answer:
The correct option is a. Catherine blames Edgar Linton for her illness in Chapter 15 of Wuthering Heights, citing the stress caused by his enmity with Heathcliff and the tension it created.
Step-by-step explanation:
In Chapter 15 of Wuthering Heights, Catherine blames Edgar Linton for her illness. She argues that Edgar and Heathcliff's enmity has placed her in the middle of a stressful situation, which has exacerbated her suffering.
Catherine believes that if Edgar could have been more understanding and accepting of her deep and complex bond with Heathcliff, the resulting peaceful situation would have been less taxing on her health.