试述票据抗辩及其种类和限制。

In October 2008 while Artai Construction Co Limited (Artai Co) was building a residence project, a serious accident took place because of geological causes. To rescue the project many construction materials, such as cement and sand, were needed. However, it was impossible for Artai Co to fi nd such a huge quantity of construction materials in a very short period of time. Artai Co, under such circumstances, had to negotiate with a developer of the neighbouring project and fi nally reached an agreement to buy construction materials from the developer at a very high price, three times the normal market price at that time. Artai Co fell into fi nancial diffi culty as a lot of funds had been spent on the rescue work and failed to pay the price for the construction materials as agreed. A dispute arose between Artai Co and the developer. Required: Answer the following questions in accordance with the relevant provisions of the Contract Law of China, and give your reasons for your answer:

(a) State the validity of the agreement between Artai Co and the developer with respect to the purchase of the construction materials, and who would decide the validity of the agreement; (4 marks)