【正确答案】The instructor presents a lecture about how ants collect water and transport it to their nest. Ants have at least two ways to gather water.
One way is for them to carry water drops on their backs. A considerable number of ants working together can carry the drop without breaking or spilling any all the way to their nest.
The other method is to wait until a large amount of water collects on a leaf. The leaf is like a container with water inside. Then a team of ants carry the water container back to the nest.

【答案解析】[听力原文]
W: We'll take up where we left off last time, talking about life inside the ant nest. One of the needs the ant community has is water. True, ants drink very little water. They get most of their water from food. But they have other uses for water, particularly keeping their eggs moist in dry climates. So the ants have a problem: how to get water back to the nest? There are two ways ants transport water.
The first method is for ants to carry water drop-by-drop on their backs to the nest. Usually they find such water standing in drops on leaves after a rain or a dew. But how do ants carry a drop without a bucket? Well, ants are tiny, but most of them getting together are able to carry the drop and thus transport water to their nest. Sometimes, of course, the drop does break and gets mostly lost to the ants.
The second method is a bit more complicated. Some species of ants will wait until a good deal of water collects in one place, like on a cupped leaf or on a bird feather. When a large amount has collected, the large number of ants will then carry the leaf or feather back to the nest. This method gets a great deal of water for the ants at one time.

Alternative Wording(替换表达)
Synonyms (a)nest—colony (b)carry—lug
Paraphrases The other expedient is to bide their time till sufficient water collects on a leaf, feather, etc.