客户身份证件或身份证明文件一旦过期后，客户之前的业务委托也随之无效。

到目前为止，货币的发展经历了以下几个阶段[ ]

A．商品--货币--纸币--信用货币

B．等价物--一般等价物--货币--铸币

C．货币--铸币--纸币--电子货币

D．信用卡--自动柜员机--电子转账终端--虚拟货币

Khanh is the manager of a shop that sells high quality paintings and reproductions of famous artworks. On 1 November she wrote to Kim and Suong, two established customers, offering the opportunity to purchase reproductions of a painting by a famous artist, each signed by the artist. The letter specifi ed a price of 10 million dong.Khanh’s fi rst letter was to Kim. However, immediately after sending the letter, Khanh discovered she had mis-typed the price as 1 million dong. Khanh immediately wrote another letter withdrawing the offer and stating the correct price of 10 million dong. Both letters were received by Kim in the same delivery. Kim wrote back to Khanh immediately accepting the offer of 1 million dong.Suong replied to Khanh’s letter stating that she would be delighted to accept the offer, but as she was given a 15% discount for her three previous purchases she assumed this would apply again. Suong wrote back to accept the offer enclosing her payment of 8·5 million dong.Khanh subsequently sold the painting to Ngoc for the full price of 10 million dong.Required:

(b) Explain whether Khanh has entered into a legally binding contract with Suong and/or Ngoc. (5 marks)

在飞机起飞或降落时，有的乘客通常会咀嚼口香糖或不断做吞咽动作，这样做的目的是使             张开，以保持               内外的气压平衡，防止其损伤。 

唯一能通过胎盘的免疫球蛋白是( )

A．IgG
B．IgA
C．IgM
D．IgD

周邦彦的《过秦楼》中写道：“水浴清蟾，叶喧凉吹，巷陌马声初断。”请问词中的“清蟾”是指什么？