A、Each flock of butterflies lays eggs in the same states. B、They start to lay eggs when they are nine months old. C、Each generat

Monarch butterflies, the large origin black insects, are a common summer sight in the northern United States and Canada. They brighten in parks and gardens as they fly among the flowers. What makes monarch butterflies particularly interesting is they migrate, all the way to California or Mexico in back. They are thought to be the only insect that does this. Every year in the late summer, monarchs begin their migration to the south, those heading for Mexico go first for the Louisiana Mississippi region. Then they fly across to go for Mexico into Texas. Once in Mexico, they establish themselves in one of about 15 sizes in the mountain forest. Each side provides the winter home for millions of monarchs. The butterflies are so numerous that they often cover entire trees. When spring comes, they began their long journey north. The question is often asked whether every butterfly makes the round trip journey every year. And the answer is no. The average monarch lives about nine months. So when flying north, they might lay eggs in Louisiana and die. The eggs of that generation may be found in Kentucky, the eggs of the next generation may be in Wisconsin or Michigan. The last generation of the season about the forth will make the journey back to Mexico and restart the cycle. Scientists learn about monarch butterflies’ migration by capturing and placing identifying tags on the insects. By recapturing the attempt of the monarch and noting where they came from, the next scientist can figure out things like butterfly’s age and its routine.
19. What is unique about the monarch butterflies according to the speaker?
20. Where do monarch butterflies settle at the end of the migration?
21. What does the speaker say about monarch butterflies’ reproduction?
22. What is the talk mainly about?