Explain or state briefly the rule or reason for your answer.

1. In a contract containing an option period, when is the offerer not allowed to withdraw his offer even before acceptance by the offeree? When is the offerer allowed to withdraw his offer even after acceptance?
2. S sold his house to B believing that B was C. Can S legally withdraw from the contract on the ground of mistake?
3. S agreed to deliver to B 500 cavans of rice at P600 per cavan. S delivered only 490 cavans deliberately misrepresenting that the delivery consisted of 500 cavans. Can B ask the court to annul the contract on the ground of fraud?
4. S sold to B a commercial land for P1,000,000. S assured B that it is certain that in two years time, the land would increase in market value by 50% or P1,500,000. It turned out that the market value of the land even decreased to about P800,000. Is S liable to B for misrepresentation?
5. Suppose in the same problem, what S sold to B, hardware owner, are 500 bags of cement. S had every reason to believe that the price of cement would go down. After two weeks, it did go down. Has B the right to have the sale annulled?

Thank you!