Robert and Peter study in the same university. They do everything together and help each other. But they often play jokes on each other. The school year was over last month and they decided to travel through the country in America. They drove a car and could stop wherever they were interested in and started whenever they wanted. Of course they enjoyed themselves. It was very hot one day and they were both hungry and thirsty. They stopped in front of a restaurant by the road. They came in, sat down at a table and ordered some dishes. Robert looked around and found there was a small bowl on the table. He thought there was some ice cream in it and took a spoonful of it and put it into his mouth. Immediately he knew it was mustard ,but it was too late. Tears ran down his face, but he pretended nothing had happened. The other young man, seeing his friend crying, asked, "What are you crying about, Robert?" "I'm thinking of my father who was hanged twenty years ago," was his reply. After a while, Peter made the same mistake. Tears ran down his cheeks, too. And his friend asked him why. "I wonder why your father hadn't been hanged before he got married!" Robertdidn'ttellPeteritwassomemustardinthebowlbecause  _  .
hewantedhisfriendtorepeatthemistake. hedidn'tknowhisfriendhatedit. hethoughthisfriendknewwhatitwas. hethoughthisfriendwasinterestedinit.
Question: Robert and Peter study in the same university. They do everything together and help each other. But they often play jokes on each other. The school year was over last month and they decided to travel through the country in America. They drove a car and could stop wherever they were interested in and started whenever they wanted. Of course they enjoyed themselves. It was very hot one day and they were both hungry and thirsty. They stopped in front of a restaurant by the road. They came in, sat down at a table and ordered some dishes. Robert looked around and found there was a small bowl on the table. He thought there was some ice cream in it and took a spoonful of it and put it into his mouth. Immediately he knew it was mustard ,but it was too late. Tears ran down his face, but he pretended nothing had happened. The other young man, seeing his friend crying, asked, "What are you crying about, Robert?" "I'm thinking of my father who was hanged twenty years ago," was his reply. After a while, Peter made the same mistake. Tears ran down his cheeks, too. And his friend asked him why. "I wonder why your father hadn't been hanged before he got married!" Robertdidn'ttellPeteritwassomemustardinthebowlbecause  _  .
A. hewantedhisfriendtorepeatthemistake.
B. hedidn'tknowhisfriendhatedit.
C. hethoughthisfriendknewwhatitwas.
D. hethoughthisfriendwasinterestedinit.
Answer: