题目

质量为m的物体，在水平力F的作用下，在粗糙的水平面上运动，下列说法中正确的是(    ) A．如果物体做匀速直线运动，F一定对物体做正功 B．如果物体做减速直线运动，F一定对物体做负功 C．如果物体做减速直线运动，F可能对物体做正功 D．如果物体做加速直线运动，F一定对物体做正功  答案：ACD阅读下面的短文，然后根据短文内容回答问题。Britons are well known for the amount of tea that they drink. The average (平均) person in the UK consumes (消费) around 1.9 kg of tea every year. That’s around 876 cups of tea. Tea is drunk by all sections of society. But tea is not native to Britain. Most tea is grown in India and China. So, how did it become an important part of British culture?Tea arrived in London in the 1600s. At this time, British ships were exploring the world and came across the drink in China. It was not long before green tea was available to buy. However, this was only available to the richer sections of society.At the beginning of the 1700s, the amount of tea arriving in Britain increased gradually. Black tea arrived at this time. At first, people drank this tea exactly as it was in China. They soon discovered that it mixed really well with a little milk and sugar, giving the drink a special British characteristic (特色).In the 1800s tea was still a product enjoyed only by people with money. At this time, they began to have “afternoon tea”. This involves (包含) drinking tea with a snack around 4 pm to avoid feeling hungry between lunch and dinner. It is a tradition that is still going today.In the late 1800s, the price of tea decreased sharply as more tea began to arrive on ships from India and China. It was no longer a drink just for rich people. Tearooms started to appear across the country. People enjoyed drinking tea and socializing in these places. At the start of the 20th century, Britons began to make tea in their homes whenever they felt like it.【1】How many cups of tea does average person drink each year in the UK?【2】What should be mixed with tea to make it a special British characteristic?【3】Why do British people have afternoon tea?【4】Could most people in Britain afford tea in the late 1800s?【5】Where did Britons enjoy drinking tea and socializing?