A、In March. B、In October. C、In August. D、In April. A细节题。浏览选项可知，该题考查时间。对话中，男士说到San Juan Capistrano的燕子always return on the same da

M: So, Rebecca, what did you do for spring break?
W: I went to southern California. I was in Los Angeles and San Diego. And I stopped in San Juan Capistrano. That’s south of Los Angeles and north of San Diego. I happened to be there just about the time the swallows returned.
M: Oh, I’ve heard about that ― they always return on the same day, don’t they?
W: That’s right, on March 19th. And they always fly away on the same day, October 23rd. In the meantime, they migrate over 7,000 miles to get to their winter homes.
M: 7,000 miles! And they always come back on the same day!
W: Yes, except for one year, a long time ago they were delayed by a storm at sea. Besides, San Juan Capistrano suffered a disaster once.
M: Once? What happened to it?
W: It was destroyed by an earthquake almost 200 years ago. But there was an old adobe church that survived. The swallows built their nests in the walls and towers of that church.
M: You were lucky to be there on the day of the year when the swallows returned.
W: Well, I wasn’t there exactly on that day. I got to town a couple of days later, but I did see the parade celebrating the swallows’ return.
M: They had a parade? The people there must really like those swallows.
W: Sure. They bring lots of tourists to town, and besides, the swallows eat insects including mosquitoes!
Questions 19 to 22 are based on the conversation you have just heard.
19. Where is the town of San Juan Capistrano?
20. When do the swallows return to San Juan Capistrano?
21. Why didn’t the swallows come back on the same day as usual one year?
22. Where did the swallows build their nests after the earthquake 200 years ago?