Task: Question Answering
Input (English): Passage: The Slaters of Wolverhampton are plagued with Mrs. Slater's chronic debilitating asthma and her cooking limited to what comes in canned goods that she can heat in boiling water. Mr. Alan Slater is sick with worry and has a cantankerous personality. Nigel longs for a life that is more than a succession of canned-food dinners made from what can be heated in boiling water. When dinner is burnt, the standard substitute of toast is always served. He loves toast, with the crunchy outside giving way to buttery softness inside. Despite her infrequent forays into cooking meals from scratch, his mother's attempts to improve her cooking change nothing before or after her death. His father continues in widowhood with the same cooking style and frequent dinners of toast. The experience brings Nigel to conclude that he is not liked. Nigel learns from a friend that the way in which he could attempt a better relationship with his father is to cook a meal for him.
His cooking efforts are thwarted by the new housekeeper, the married and "common" Mrs. Joan Potter, who seduces Alan with her apple pie and array of gourmet meals. The two start to spend time together: at one point, she exiting her council house through an upstairs window so as not to be found out by her husband. Without announcement, the Slaters move to the Herefordshire countryside along with Mrs. Potter. Nigel co-exists with her but never accepts her. She makes a competition of cooking when the teenaged Nigel's shows an emerging interest in developing his skills at school home economics class cookery lessons. Mrs. Potter's lemon meringue pie becomes Nigel's quest to learn the secret recipe. 
Question: While Nigel's mom has asthma, what makes his dad ill?
Output (English): worry.