单项选择题 My friend is a taxi driver. He has been a taxi driver for ten years. It’s a nice job most of the time. He can meet a lot of people. He always works at night because there is too much traffic during the day. He usually goes home between two o’clock in the morning. There are some very strange things, which often happen at night. One day my friend was taking a woman back home from a party at three o’clock in the morning. She had her little dog with her. When they got to her house, she found she had lost her key. So my friend waited in the car with the dog while she climbed in through the window. My friend waited and waited. After half an hour of knocking, he decided to find out what was going on. He tied the dog to a tree and started to climb in through the window. At that moment some policemen came. They thought my friend was a thief. Luckily, the woman came downstairs. She must have gone to sleep and forgotten about my friend and the dog.A.your boatB.the storeC.the shipD.the hotel

单项选择题 抗肿瘤免疫的主要效应细胞是（）

单项选择题 下面与胚胎抗原无关的是（）