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问题 单项选择题

下列关于限制酶和DNA连接酶的理解正确的是（）

A.其化学本质都是蛋白质

B.DNA连接酶可以恢复DNA分子中的氢键

C.它们不能被反复使用

D.在基因工程操作中可以用DNA聚合酶代替DNA连接酶

答案

参考答案：A

选择题

Rt△ABC中，∠C=90°，AC=3，BC=4，CD⊥AB于D点，以C为圆心，3cm为半径作⊙C，则AB与⊙C的位置关系是（　　）

A．相离

B．相切

C．相交

D．无法确定
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问答题

ABC Limited is a private company limited by shares, which has adopted Table A as its articles of association. The authorised and issued share capital of ABC Limited is EUR 10,000 divided into 5,000 Class ‘A’ shares of EUR 1 each and 5,000 Class ‘B’ shares of EUR 1 each. Class ‘A’ shares enjoy preferential rights over dividends and repayment of capital. Mary holds 4,000 Class ‘A’ shares and 4,000 Class ‘B’ shares; Tim holds 500 Class ‘A’ shares and 1,000 Class ‘B’ shares; and John holds 500 Class ‘A’ shares. Mary wishes to remove the preferential rights attached to Class ‘A’ shares but Tim opposes.Required:Advise Tim. (10 marks)
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