He had something to write down and asked me for _________．

A．a paper                                                   B．some papers

C．some pieces of paper                                  D．a piece of paper

I went home one Saturday afternoon in the autumn of 1993 to get some work done in the garden. While sweeping leaves on the ground, my five-year-old son Nick came over and asked me to write something on a piece of paper to make a sign for him.
"What for?" I asked.
" I’m going to sell some of my stones, " he answered.
Nick was fascinated with stones and had collected many stones from all over.
" I’m too busy to do that for you. Go and ask your mum for help," I said.
A short time later, Nick, returned with a sign, reading, " Stones, One Dollar Each". He took the sign, a small chair and 4 of his best stones and walked to the road in front of our garden. There he put the stones in a line and sat down on the chair.
After half an hour, nobody passed by. I walked to him and asked him to go back, but he didn’t.
Another half hour later, a small car came down the road. I watched as Nick stood up, holding his sign up. A woman rolled down a window and read the sign. I couldn’t hear their talk, but I saw the woman turn to the driver and the man reach for his pocket.
I sat in the yard, as Nick ran to me. Waving the dollar, he shouted, "I told you I could sell one stone for a dollar -- if you believe in yourself, you can do anything. "
【小题1】Why didn’t the writer help his son?

I went home one Saturday afternoon in the autumn of 1993 to get some work done in the garden. While sweeping leaves on the ground, my five-year-old son Nick came over and asked me to write something on a piece of paper to make a sign for him.                       
“What for?” I asked.
“I’m going to sell some of my stones, " he answered.    
Nick was fascinated with stones and had collected many stones from all over. “I’m busy to
do that for you. Go and ask your mum for help." I said.
A short time later, Nick returned with a sign, reading. " Stones. One Dollar Each”. He took the sign, a small chair and 4 of his best stones and walked to the road in front of our garden. There he put the stones in a line and sat down on the chair.
After half an hour, nobody passed by. I walked to him and asked him to go back, but he didn't.
Another half hour later, a small car came down the road. I watched as Nick stood up, holding his sign up. A woman rolled down a window and read the sign. I couldn't hear their talk, but I saw the woman turn to the driver and the man reach for his pocket.
I sat in the yard, as Nick ran to me. Waving the dollar, he shouted. "I told you I could sell one stone for a dollar — if you believe in yourself, you can do anything."
【小题1】Why didn't the writer help his son?