The correct answer is the rabbit.
In this food chain, the grass, since it is a autotrophic organism is the producer.
The rabbit is a herbivore that feeds on the grass, making it the primary consumer.
The snake is a carnivore that feeds on the herbivore, making it the secondary consumer.
In the end, the hawk is a carnivore that feeds on another carnivore, the snake. Therefore, the hawk is a tertiary consumer.