Khi nói về dao động cơ cưỡng bức, phát biểu nào sau đây là đúng?

A. Dao động cưỡng bức có tần số nhỏ hơn tần số của lực cưỡng bức.

B. Dao động cưỡng bức có biên độ không đổi và có tần số bằng tần số của lực cưỡng bức.

C. Dao động của con lắc đồng hồ là dao động cưỡng bức.

D. Biên độ của dao động cưỡng bức là biên độ của lực cưỡng bức.

Read the passage about clothes, then answer the questions below.

Clothes can tell a lot about a person. Some people like very colorful clothes because they want everyone to look at them and they want to be the center of things. Other people like to wear nice clothes, but their clothes are not colorful or fancy. They do not like people to look at them. Clothes today are very different from the clothes of the 1800s. One difference is the way they look. For example, in the 1800s all women wore dresses. The dresses all had long skirts.

But today women do not always wear dresses with long skirts .Sometimes they wear short skirts. Sometimes they wear pants. Another difference between1800s and today is the cloth. In the 1800s, clothes were made only from natural kinds of cloth. They were made from cotton, wool, silk, or linen. But today, there are many kinds of man–made cloth. A lot of clothes are now made from nylon, rayon, or polyester.

What is another difference between 1800s and today?

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