原式=2x(x+y)(x-y)×(x+y)(x-y)xy=2y，
当y=2时，2y=22=2．
Chien, Linh and Trang formed a new limited liability company in January 2011. They decided that the company would specialise in selling high quality food products. Before the company was formed, Chien, Linh and Trang decided to enter into several transactions so that the company could commence trading as soon as the legal formalities relating to formation had been finalised.Chien was responsible for sourcing and selling seafood. In October 2010 he ordered 500 boxes of crab meat with the intention of selling it to the customers of the new company. He wrote to 50 prospective customers of the new company informing them that a maximum of three boxes of crab meat would be available for purchase by each customer at a price of 20 million dong per box. The remainder would be advertised for general sale.Linh was responsible for sourcing and selling herbs. She secured an agreement with a supplier of saffron, an expensive herb, and has already been told informally by five of her restaurant contacts that they would be prepared to pay 30 million dong per box for this product. She sent a box of saffron to each customer with an invoice for 30 million dong in November 2010.Trang agreed to take responsibility for sales of luxury chocolates. He had little knowledge of the products, but in December 2010 entered into an agreement with a Vietnamese trader to purchase 1,000 kilos of chocolates specially imported from Switzerland.Required:
(a) Explain whether legal binding contracts have been formed on behalf of the company by the actions of Chien, Linh and Trang, and the rights and obligations created by their actions. (7 marks)
我国目前的供电系统多是（）。
A.单相两线式
B.单相三线式
C.四相三线式
D.三相四线式
