Q: Read the following article and answer the question. Article: The summer vacation is over. It's true that time flies. In the vacation, the weather was very hot, but I enjoyed myself. I did my homework in the morning. I got up at 6:30a.m. and took a walk in the garden for half an hour. After breakfast I began reading English and Chinese and did some math exercises. It usually took me three hours or more. I worked quite hard and I made great progress . I spent the afternoon outside. I went swimming and it was fun. I would not go home until it was about five or six o'clock. Sometimes my friends came to see me and we spent some time listening to music. In this way I spent my vacation happily. I not only studied hard, but also became a good swimmer. Now I'm in good health and high spirits . Question: The writer spent most of the afternoon _ . Answer:

Available choices: (I) listening to music; (II) visiting his friends; (III) walking in the garden; (IV) swimming;
A:
(IV)