ZAO Picture is a specialist company that deals in works of art. It acquired three paintings signed by a famous artist and decided to make these available for sale.The company sent letters to Nikolai, Peter and Svetlana stating the following:‘ZAO Picture is prepared to offer you an exclusive bargain. You have the opportunity to purchase a signed painting (full description given) by the famous artist Chaikin for 500.000 roubles. In order to secure your purchase please reply, enclosing full payment, by 13.00 hours on 1 February 2008’.Nikolai replied to the letter and sent full payment for the painting, but his reply did not reach ZAO Picture until 3 February 2008. Peter’s response was to send a remittance of 450.000 roubles, with a letter stating that he was prepared to purchase the painting but as a valued customer expected a discount of 10%. Svetlana did not reply, but the general director of ZAO Picture was certain that as an enthusiastic art collector she would wish to accept the offer and sent her a painting with an invoice for 500.000 roubles.Required:

(a) Explain whether the letters sent by ZAO Picture to the three clients were offers which, if accepted, formed the basis of binding contracts. (4 marks)

（）可把回转运动变成直线运动或把直线运动变成回转运动。

A.直齿轮传动

B.齿条传动

C.斜齿轮传动

D.圆锥齿轮传动