Answer:
The correct answer is option D which is keystone.
Step-by-step explanation:
Keystone is the important specie in the food chain, if this specie is removed from the food chain the food will be disturbed and ruining the niche of other species which are dependent on the keystone.
Here tigers are the keystone prey. Their removal causes disruption in the population of their predator as well as the whole food chain.
The increase in the population of gazelles and as a result of this decrease in resources for gazelle species and disruption in other species in food chain indicates that tigers are keystones.