T1I2

7/10

10Step 11. Listen to the dialogue from the previous day.2. Go back to page 7, Step 4 and play the man’s part again.Step 2Read the passage and choose the best answer from among the four choices for ques-tions 1 to 4.CD1-02CD1-035101520DAY2の解答・解説は別冊「解答・解説」のp.4～6In spring to early summer, every 13 or 17 years, some parts of eastern North America witness a mysterious phenomenon that cannot be seen anywhere else. Peri-odical cicadas crawl out en masse after having spent their juvenile years in subterra-nean hideouts. Millions, or sometimes billions, of mature nymphs climb up trees, molt for the last time and become adults; then they mate, lay eggs, and die, all in a few weeks.What distinguishes periodical cicadas from other cicada species are their life cy-cles. There are about 3,000 cicada species worldwide. They spend years under-ground, and only a relatively short period as fl ying adults. Most cicada species have life cycles of between two and eight years and some members appear above ground every year, so they are sometimes referred to as annual cicadas. Periodical cicadas, however, have lifespans of 13 or 17 years, making them the longest-lived insects known. Also, a whole brood develops synchronously and emerges from the soil all at once, sometimes with a density of more than 1.5 million per acre, then disappears until the next mass emergence.How did their life cycles evolve to become synchronous? Why are they so long? Why the prime numbers? For centuries, these questions have intrigued entomolo-gists, and they have produced various theories and hypotheses.For example, one theory explaining their synchronized mass emergence is the survival strategy called “predator satiation.” Periodical cicadas are vulnerable. They Review of the Previous DayRead the PassageThe Mysteries of Periodical Cicadas10WEEK 1 DAY 2ReadingReading for Comprehension