Do you know dolphins and believe they are among the smartest animals?

    Dolphins are mammals (哺乳动物), not fish. The most famous type is the Bottlenose Dolphin. Bottlenose Dolphins are the stars of many shows. Their mouths look like friendly smiles and they can be trained to play tricks by their trainers. Like other dolphins, they breathe air through the blowholes on top of their heads from the water surface. They also give birth to babies and feed their babies milk. Dolphins can communicate through whistles (哨音) and even call each other, using special names formed by different series of whistles. Noises also help them find food. Dolphins make up to 1,000 clicking noises per second. These clicks travel underwater until they hit an object and return to the dolphin, showing the object’s size, shape and location.

    Humans have studied dolphins for years to learn how their brains work. A lot of research has been made to study dolphins in the wild. For example, people have seen dolphins off Australia’s coast use shells to catch fish. It shows that dolphins are good at using tools.

    It is said that smart animals like to play. If so, dolphins win the gold medal for their playfulness. They can jump out of the water up to 16 feet, play amazing tricks and ride the waves.

    Scientists give different reasons for play. They find that play helps animals grow mentally and physically. The animals learn their own limits and abilities, practice skills and gain confidence. So, when you see dolphins playing in the wild, you’ll know that they are not just playing for fun, but also to practice their skills and stay healthy.

1.1. What is Paragraph 2 mainly about?

A An introduction to a kind of dolphin.

B Reasons why dolphins play in the wild.

C Differences between mammals and fish.

D The way dolphins communicate with each other.

解析：选A。A 主旨大意题 第二段首句即指出“最著名的种类是宽吻海豚”，随后整段围绕宽吻海豚的外形特征（如似微笑的嘴）、生理特点（用气孔呼吸、哺乳）、沟通方式（哨音、回声定位）展开，因此本段核心是介绍这一具体种类的海豚，而非泛论所有海豚或仅聚焦沟通方式。

2.2. What ability of dolphins does the underlined word “It” in Paragraph 4 refer to (指代)?

A Calling each other.

B Using shells to catch fish.

C Jumping out of the water.

D Playing amazing tricks.

解析：选B。B 词意指代题 第四段中，“It”指代前一句“人们曾观察到澳大利亚海岸附近的海豚用贝壳捕鱼”，这是一个具体事例，用以说明海豚擅长使用工具的能力，故答案明确为“使用贝壳捕鱼”。

3.3. How does the writer prove that dolphins are among the smartest animals?

A By presenting facts.

B y carrying out a survey.

C By comparing numbers.

D By interviewing trainers.

解析：选A。A 推理判断题 全文通过列举事实来证明海豚的智慧：如用哨音命名、回声定位觅食、使用工具捕鱼、通过玩耍锻炼能力等，并未采用数据对比、调查或访谈的方法，因此是“通过呈现事实”来论证。