Narrator: Listen to part of a lecture in a biology class. Professor: Today we’re going to talk about a fascinating adaptation in some desert plants, specifically the phenomenon known as 'seed dormancy.' In many arid environments, rainfall is unpredictable. A plant that germinates too early, after a light rain, might not survive if a drought follows. So some species have evolved a clever strategy: their seeds remain dormant until a significant amount of rain has fallen, washing away inhibitors in the seed coat. This ensures that germination occurs only when there’s enough moisture for the seedling to establish. But here’s an interesting twist: in some species, the seeds also require a period of high temperatures, like a summer heat wave, to break dormancy. This double trigger—heat and then sufficient water—prevents seeds from germinating in the fall, when a brief rain might be followed by cold, killing the young plant. So, dormancy isn’t just a passive state; it’s an active, tuned response to environmental cues.
❓ Вопрос What is the main purpose of the double trigger mechanism described by the professor?
A. To ensure seeds germinate only after a single heavy rain
B. To prevent germination during unfavorable conditions, such as after a light rain in fall
C. To speed up germination in all types of weather
D. To allow seeds to germinate without any water
✅ Правильный ответ
To prevent germination during unfavorable conditions, such as after a light rain in fall
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word
