读句子,用am, is , are 填空。
1. I _______ a boy, you _______ a girl, we ________ friends.
2. He ________ a student, she _____ a student, too. They ______students.
3. I _______ helpful at home, my father _______ helpful, too.
4. My brother _____ tall, my sister _____short, but they ______ all(都) thin.