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能特异性识别抗原的免疫细胞有
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按功能不同可将T细胞分为
B细胞的主要功能有
1. Listen to the dialogues and fill in the blanks.Words and Expressionsconvenient方便的open an account开户online bank网上银行revolution改革；革命simulate模仿rush hours交通拥挤时间traffic jam交通拥堵get off work下班Dialogue 1S:Aunt Cindy, do you shop①often?C:Yes. It’s very convenient and the price is even②.S:Last week, I tried to buy some books online, but I didn’t know how to pay for them.C:You should open an account at the online bank first.S:Are there many things online?C:Sure. You can find things all over the③. Let’s check it out online!S:That’s amazing. Oh, an online virtual supermarket?C:Let’s④to check it out.S:Oh, I got it. It simulates the real supermarket, which makes it feel so real. Mom will love it. She loves shopping in supermarkets.C:No doubt about it. Shopping online will get more and more⑤. It’s a real revolution about people’s consuming habits.Dialogue 2A: Here we are on the subway.M: Yes, we are travelling in rush hours. It could be very crowded in the⑥and after 6 o’clock in the afternoon.A: I heard that many people⑦.M: Yes, many families have their own cars.A: Why don’t they drive? Isn’t a car more convenient than the subway?M: Well, it is⑧to find a parking place in the city. Besides, parking is expensive in the downtown.A: I see. I saw many public bicycles⑨the subway station. I think we can go back home by bike⑩.M: OK. Bike riding will help us do some exercise. And we won’t have to worry about traffic jam after getting off work.
设有关系S（S#，SNAME，AGE，SEX）请用关系代数表达式表示写列查询语句查询所有的男生信息σ____='____'( _______)
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