根据短文内容的理解，选择正确答案。
I didn't think I had a passion(激情). I would sit in front of the TV all day, thinking about nothing but the next show. It was not long ago that I first learned how important having a passion is to life.
That day I went with my mum to drive my sister to the gym. I was bored. Then, as my mum stopped at a red light, someone on the side of the road caught my eye（吸引我的世界）. It was a man dressed in rags (衣衫褴褛). He was homeless. That didn't interest me, for I had seen many like him before.
But in some ways he was different. This man was not sitting down with a sad expression(表情). He had a radio in his hand and was dancing happily to the music. The radio seemed to be the most precious(珍贵) thing he had.
"Mum, why does that man have a radio even thought（尽管） he's homeless?" I asked.
"He bought it," she replied. I was still unable to understand.
"But if he's homeless, why doesn't he use the money to buy food or clothes? He wasted it on something he doesn't need."
"Well, Sarah, sometimes food and clothes aren't the most important things. We need happiness, too."
The man must care too much about music to buy a radio instead of food clothes. I soon realized（意识到） that happiness is the key to life. Without it, there's nothing to look forward to.
Since then I've never gone a day without thinking of what's truly important. A home, a meal, clothes—these things are only part of the picture. What's often forgotten is that we all need a pleasure, a light in a dark day. We all need a passion.
；如果将该木块放在此水平面上，初态静止但是可以自由滑动，同样的子弹以同样的速度v0水平飞来，刚好能够透木块并使二者共速运动。在上述两个过程中，如果子弹受到阻力大小完全相同，穿孔的深度也完全相同，则 （ ）
