()3.A duck ______ swim in the river.
A.can't
B./
C.can

【解析】：本题考查情态动词的用法。根据常识，鸭子会游泳，这是一种能力。“can”表示“能，会”，符合语境。A选项“can't”表示“不能”，与事实不符；B选项不填动词，句子结构不完整，缺少谓语动词。所以正确答案是C。
【答案】：C

()4.—What is it doing?
—______ eating fish.
A.It's
B.It
C.Is

【解析】：问句“What is it doing?”是现在进行时，询问“它正在做什么？”，回答也应使用现在进行时，其结构为“主语+be动词+动词-ing形式+其他”。这里主语是it，be动词用is，所以应填“It's”，A选项正确。B选项缺少be动词，C选项是疑问词，均不符合语法。
【答案】：A

()5.The frog(青蛙) is ______.
A.jumps
B.jump
C.jumping

【解析】：本题考查现在进行时。句意为“青蛙正在跳”，现在进行时的结构是“be动词+动词的现在分词”，is是be动词，后面应接jump的现在分词jumping。A选项jumps是第三人称单数形式，B选项jump是动词原形，均不符合现在进行时的结构，所以选C。
【答案】：C

四、用所给单词的适当形式填空。
1. I can () in the sea in summer. I usually go () with my friends in summer.
2. She () our friend. We () playing together.
3. —Is this () pen?
—Yes, it's ().
4. —() pencil is this?
—It's ().
5. —What are they doing?
—Wu Binbin (). Mike ().

1. swim; swimming 2. is; are
3. your; mine 4. Whose; hers
5. is eating; is drinking

五、阅读短文,回答问题。
Zip: Here we are at the sports meeting.
Zoom: Look! The baby kangaroo is running. Where is the mother kangaroo? What is she doing?
Zip: She's over there. She's looking at the monkey.
Zoom: I see the duck family. The mother duck is swimming. What about the baby duck? What is it doing?
Zip: It's swimming, too.
Zoom: Come on! Let's go and see.
Zip: Let's go!
1. What is the baby kangaroo doing?
2. Is the mother kangaroo jumping?
3. What is the mother duck doing?
4. What is the mother kangaroo doing?
5. Is the baby duck swimming?

1. It's running.
2. No, she isn't.
3. She's/It's swimming.
4. She's looking at the monkey.
5. Yes, it is.