综合写作：
Pine trees in the American Northwest are sometimes attacked by the mountain pine beetle. The beetle burrows in the tree’s bark, preventing the tree from moving water and nutrients through its trunk effectively. Fortunately, there are several factors that naturally limit the damage the mountain pine beetle causes to pine tree forests.
First, winter temperatures in many areas in the American Northwest keep the population of mountain pine beetles small. Young pine beetles need to survive the winter in a larval state to emerge in the spring and begin feeding on the trees. Because winter temperatures in the Northwest drop well below freezing for extended periods, the great majority of beetle larvae freeze to death. This natural die – off keeps the beetles’ numbers in check.
Second, the pine trees attacked by the pine beetle can fight back and survive by flushing out the beetles with sap. When a beetle bores into a tree, the tree’s natural response is to fill up the hole with sap or pitch, a sticky, gluelike substance. Beetles caught in the sap flow are flushed out of the tree before they can inflict lasting damage. This defense against the beetles ensures that most trees will survive an attack.
Third, the beetles typically feed on mature trees with trunks more than twelve centimeters in diameter and avoid younger trees. In the pine forests in the Northwest, young pine trees are plentiful thanks to occasional natural fires. Natural fires create clearings in the forest, providing young trees with access to sunshine and helping them develop. Thanks to the healthy balance of young and mature trees in the Northwest pine forests, mature trees killed by pine beetles are quickly replaced by young trees, and the forests remain more or less intact.
学术写作：
Instructions: Your professor is teaching a class on public health. Write a post responding to the professor’s question.
In your response you should do the following:
- Express and support your opinion.
- Make a contribution to the discussion in your own words.
An effective response will contain at least 100 words.
Dr. Achebe
Today’s topic is about health and how people’s health status has changed over time. Health has always been in one of people’s primary concerns in daily life. People in the past and people today view health somehow differently, but maintaining good health is always of central significance. Nowadays, thanks to modernization, quite some people think that it is easier to maintain good health today than in the past. What do you think?
Claire
I agree that it is easier to maintain good health now. We have access to more information and resources than we previously had. With advances in medicine and technology, we can quickly identify health problems and have many more treatment options. Additionally, people now have a greater awareness of the importance of living a healthy life.
Paul
I don’t think that it is easier to maintain good health now. Despite all of the advances in medicine, technology, and health education, modern society is marked by unhealthy lifestyles, leading to increased rates of obesity, heart disease, and other health problems. We have become more sedentary, with many people relying on cars instead of walking or biking.
