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I am Alice. My sister and I spent our last summer holidays with our uncle who is a geologist (地质学家) and loves to collect stones.
One day he bought us two backpacks and asked us to go to the mountain with him. We walked the whole day. Every now and then he put stones in our backpacks. To our surprise, he also took some stones out from them. But we thought he had just found better stones.
When we returned to the house, we were very tired. The backpacks were so heavy that we felt relief （轻松）when we took them off. Yet our uncle's backpack was half empty.
"Why did you give us so many stones?” we asked.
"I didn't. You did." he said. “You didn't know it, but I gave you a little attitude(态度) test today. I listened to every word you said. Whenever you were complaining (抱怨) , I added a stone to your backpacks. whenever you talked about something with positive (积极的) thinking, I took out a stone. And now look at your backpacks."
Our backpacks were full of stones.
“Your negative( 消极的) thoughts are just like stones. You carry them in your mind just like those stones in your backpacks. The mote negative thoughts you have, the heavier your mind will be.” said our uncle.
With great love, our uncle taught us one of the most important lessons it life—the power of the attitude.
磺、木炭组成。“黑火药”属于 （ ）