Which one of the following shows a unique relationship with an insect that has coevolved with it and that is the only insect that can pollinate this tree ?

Many fig tree species share a highly specific, one-to-one relationship with a particular wasp species.

This means that a specific fig species can only be pollinated by its co-evolved 'partner' wasp species.

The wasp pollinates the fig inflorescence while searching for suitable places to lay eggs. In return, the fig provides the wasp larvae with some of its developing seeds as food.

This is a classic example of coevolution, where the survival and reproduction of each species are tightly linked to the other.

Hence option (a) is the correct answer.