Optimal foraging theory suggests that: a. when search time is long relative to handling time, predators should be generalists.
b. when handling time is long relative to search time, predators should be generalists.
c. new items are added to the diet only if their handling time is larger than average.
d. specialized diets are rare in nature. e.none of the above

a. when search time is long relative to handling time, predators should be generalists.

Explanation:

In behavioral ecology, the optimal foraging theory can be used to predict animal behavior related to the search for food. Animals need to take different foraging approaches in order to obtain better energy cost benefits. This theory proposes that natural selection chose animals that maximize their adaptive fitness by adopting the better (economically effective) foraging pattern according to its environment. Moreover, animals are regarded as generalists when they are capable of surviving in many different habitat conditions and/or eat different types of foods (omnivores are generally generalist species). In this case, predators with large search times don't have time to choose between different prey, thereby they will be generalists.