Which of the following is not true regarding an offer? Select one: a. When the offerer has allowed the offeree a certain period to accept, the offer maybe withdrawn at any time before acceptance by communicating such withdrawal except when the option is founded upon a consideration as something paid or promised b. An offer becomes ineffective upon the death, civil interdiction, insanity or insolvency of either party before acceptance is conveyed c. Business advertisements such as television commercials, classified ads, billboards, and brochures are considered as an offer d. The offer must be certain