| 1 | The students are working on a mathematical problem. | |
| 2 | She rubbed the exercises off the blackboard after class. | |
| 3 | And what is the shape, for one more clicker question on ammonia? | |
| 4 | A simple exercise helps support our hypothesis. | |
| 5 | You can find the answers of all the exercises at the end of this book. |
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