which of the following is keystone species?

1. fig
2. deer
3. mycorrhiza
4. pollinator

The correct answer is 1.
The common fig (Ficus carica) is a species of flowering plant in the genus Ficus, from the family Moraceae, known as the common fig. It is the source of the fruit also called the fig, and as such is an important crop in those areas where it is grown commercially. Native to the Middle East and western Asia, it has been sought out and cultivated since ancient times, and is now widely grown throughout the temperate world, both for its fruit and as an ornamental plant.