题目

关于记忆细胞形成的叙述中，正确的是(  ) A．只由部分B细胞形成 B．只由部分T细胞形成 C．B细胞和T细胞都不能形成 D．B细胞和T细胞都能形成 答案：D 解析: 在细胞免疫和体液免疫过程的第二阶段，即反应阶段，无论是B细胞还是T细胞受到抗原的刺激后，都要经过一系列的增殖、分化，形成成熟的效应B细胞或效应T细胞，同时，都有一小部分B细胞或T细胞形成相应的记忆细胞。当同一种抗原再次进入机体时，记忆细胞都会迅速增殖、分化，形成大量的完形填空 Dear Editor, 　　I am w ____1____ to say that I am a ___2_____ building a new zoo in our town. Zoos are terrible places for a___3__ to live. I've v____4____ a lot of zoos in my life, and I have never seen one I liked or one t___5_____ was suitable for animals to live in. Just last week, I visited a zoo and couldn't b ____6____ what I saw. The animals are k ____7____ in tiny cages and can h ____8____ move at all. And they are only given food once a day. Is this good way for animals to l ____9____? I don't think so. Sincerely, Disgusted