Which of the following marks would be considered arbitrary?

A mark is considered arbitrary when it is a common term that has no relation to the goods or services with which it is associated. In this case, "Apple" is a common fruit and has no inherent connection to computers. Thus, using "Apple" as a brand name for computers makes it arbitrary. Arbitrary marks are strong trademarks because they are distinctive and can effectively identify a single source of goods or services.

On the other hand, the other choices consist of suggestive or descriptive marks. "Cold" for ice cream suggests a characteristic of the product, associating the temperature aspect with the goods. "Fast" is descriptive for a delivery service, implying the speed at which the service operates. "Book" for literature is also descriptive, directly indicating the type of products sold. These marks do not have the same level of distinctiveness as "Apple" because they directly relate to the goods or services offered, thus they are not considered arbitrary.