综合写作：
The saber – toothed cat, which gets its name from its oversized and knifelike front teeth, was a large predator (as large as today’s tigers or lions) that lived in North America until 10,000 years ago. Some scientists have proposed that saber – toothed cats were social animals that lived and hunted in large packs. Several arguments support this theory.
Surviving Broken Bones
First, fossil evidence shows that some saber – toothed cats survived injuries such as broken bones. Serious injuries such as broken bones usually prove deadly to predators that live solitary lives and hunt by themselves. A solitary such as broken bones usually prove deadly to predators
that live solitary lives and hunt by themselves. A solitary predator prevented from hunting by an injury often dies of starvation. The fact that saber – toothed cats survived such injuries suggests that they lived in packs: an injured cat could be given food by other cats from the pack until the
injury healed and the cat could hunt again.
Tar Pit Evidence
Second, there is evidence from fossils of animals trapped in ancient tar pits. Tar pits were naturally occurring reservoirs of tar, a sticky liquid substance. When animals like deer or
antelope became trapped in tar pits, their loud cries often attracted predators; the predators then became trapped in the pit themselves and died. In many tar pits the number of
saber – toothed cat fossils is very large. Some researchers have interpreted this as the result of saber – toothed cats hunting in packs and becoming trapped in pits together.
Competition
The saber – toothed cats were not the only large predators in their habitat. They had to compete with other large predators such as wolves and lions, and both wolves and
lions were social animals. If the saber – toothed cats had lived and hunted in groups, it would have made it much easier for them to compete successfully against the other social
predators in their habitat.
学术写作：
Instructions: Your professor is teaching a class on sociology. Write a post responding to the professor’s question.
In your response you should:
- Express and support your opinion.
- Make a contribution to the discussion in your own words.
An effective response will contain at least 100 words.
Doctor Achebe
This week, we’ll be discussing ways to address air pollution. One idea is introducing environmental taxes on air travel. Such taxes, also referred to as ecological taxes or green taxes, are extra charges that get added to the price of airplane tickets. Money collected from these taxes could be invested in environmentally friendly technologies or in promoting other, cleaner modes of transportation.
Do you think there should be an environmental tax on air travel? Why or why not?
Andrew
We should impose environmental taxes on air travel. These taxes might encourage people to find cheaper, more eco-friendly ways to get places. In my country, many people use planes to fly a short distance because flights are relatively cheap. They could just as easily take a less polluting form of transportation.
Claire
Additional taxes on air travel will do little to solve the problem of air pollution. Airplane tickets would become more expensive, punishing passengers without incentivizing airlines to become more environmentally friendly. The airlines should pay the price to protect the environment, not their customers.
