阅读下面材料，从每题所给的A、B、C、D四个选项中选出最佳选项。

    Hello, I'm Lucky. I am a guide dog. I start training(训练) in a school when I am little. Being a guide dog is not easy. We have to be very smart. We need to understand orders(指令). I am very kind to people. So people trust(信任) me.

    What do I learn at school? I learn to wear a harness(导盲鞍). When the harness is on, I start my work. I can lead a person from one place to another. I stop when I see trees in front of me. And I can remember the paths.

    I know you like me and want to play with me. But I can't play with you when I am at work. You are welcome to play with me when my harness is off. That's play time.