Question: Using points and examples from the talk,

参考答案: The lecture is about bird migration, and there are two types of changes birds exhibit before actually migrating.
One change has to do with body weight: birds eat a lot and gain a lot of weight just before migrating because they have little time to look for food during the long trip. Since much energy is needed in order to fly long distance, birds will eat a lot to store fat before migration. The example the professor gives is of the red-winged blackbird, which gains about B0% more weight.
The second one is the change of social habit. Those birds are usually not sociable, but they start to flock together when migrating. Birds do this for safety reasons.
答案解析: [听力原文]
W: Today, I’d like to introduce the fascinating topic of bird migration. Bir