【正确答案】According to the lecture, some animals in tropical rainforests have developed two behaviors: searching for food alone and sending warning calls to protect their territories. First, some big mammals like apes usually search for food individually in order to avoid conflicts over struggling for food with fellow apes.
Also, the professor says that some animals like monkeys send warning signals by crying aloud to inform and keep the approaching animals away from their territory.

【答案解析】[听力原文]
W: Today we are talking about animals in tropical rainforests. Animals are like human beings; they know how to look out for themselves. Closely related to this are two activities: searching for food individually and making sounds to protect their territories.
One behavior has to do with searching for food. Some big animals need a large amount of food, such as apes. If they go foraging with others, they will certainly come into conflict when they find only a little food. Thus they have a better chance if they go out alone, which is exactly what most of the large apes do.
The other behavior concerns protecting their territory. Animals move about a great deal in their search for food. They must develop means to inform others about their territory if they want to have sufficient supply of food. For example, howlers, a type of monkey, usually protect their territory by making a screeching sound. If other monkeys or animals enter their territory, they will make a sound to tell that this is their range. And other monkeys will leave after hearing the sound.

Alternative Wording(替换表达)
Synonyms (a)tropical rainforest—jungle (b)territory—range
(c)ape—chimp, simian (d)individually—on one's own
(e)keep away from—warn off
Paraphrases 1. Some large species like apes conduct their food hunts singly with an eye to avoiding conflicts with their fellows.
2. Warning cries are an expedient that monkeys have recourse to in order to warn others off their territory.