几种原子的核电荷数如下表所示：

具有相同原子数和电子数的分子或离子叫等电子体，等电子体具有相似的结构和性质。由上表中的数据判断下列各组粒子中属于等电子体的是                               

A．NO和O₂        B．CO和N₂        C．SO₂和CO₂        D．PO₄^3—和CO₃^2-

On 3 March 2008, Azman wrote to Benny offering to sell to Benny his yacht, Lightning, for RM1 million. The letter expressly stated that if Benny did not reply by 10 March 2008, he would be deemed to have accepted the offer.On 9 March 2008, Azman sent a letter to Benny revoking his offer. On 10 March 2008 Benny posted a letter to Azman accepting Azman’s offer. Azman’s letter of revocation reached Benny on 11 March 2008. Benny’s letter of acceptance reached Azman on 12 March 2008.Benny wishes to know whether there is a valid contract between him and Azman for the sale and purchase of the yacht, Lightning.Required:Advise Benny under the law of contract. (10 marks)