效应B细胞是由B细胞和记忆细胞分化而来的，分化的原因有（   ）
①T细胞把抗原呈递给B细胞             ②抗原直接刺激B细胞 
③抗原刺激记忆细胞                     ④B细胞进行有丝分裂

阅读理解

    In certain countries of the world，the king or queen is still the head country。The UK is one of these countries。So that does the British royal family(皇室) represent for the British people today? Well，a large number of things。The royal family are of course a part of British history and tradition。They still have an important and meaning for many people today。It just wouldn't feel the same if there were no royal family。In addition to that，the queen has important formal duties：

    ●as head of the state，the Queen represents the UK on visits other would leaders to visit the UK.

    ●as head of the armed force，only the Queen can declare when the UK is at war or when the war is over。

    ●as head of the Church of England。

    Not just the Queen，the royal family spend a great deal of their time traveling up and there should be royal family。Sometimes the press and media criticize（批评）the royal family as well。One criticism is that the British people should not have to pay for the royal through their taxes。Another is that the Buckingham Palace should be open to the public more often，in order to pay for the building repairs that are necessary。