1 . 单句改错，每个句子中有且只有一个错误
1. People don’t have enough exercise are more likely to have heart attacks.
2. As is known to all, 70% of the air you breathe in every day are nitrogen (氮气).
3. With the help of the teachers, most of the students have made great progresses.
4. Though knew the truth, the witness of the case remained silent for some reason.
5. My grandma used to tell me that a losing opportunity never returns.
6. Can you help Jane out? She can’t make herself understand in class.
7. When it comes to find excuses, she is an expert with whom no one can compare.
8. Xi’an, known as Chang’an then, has become the world’s largest city by the Tang Dynasty.
9. Unfortunate, the car accident claimed two lives and left four injured.
10. Riders are often scared for the first time they get on a horse.

2 . 他坐在椅子上，看着孩子们在花园里玩耍。(observe) （汉译英）