Primary consumers are organisms that directly consume producers (plants or algae) as their source of energy. They are herbivores that feed on plants or plant-based materials.

The correct answer is option 'A' - Bird, rabbit, elephant. Let's break down the chain to understand why it contains primary consumers:

1. Bird: Birds are primary consumers because they consume plants and seeds as their primary source of energy. They may feed on fruits, nuts, and grains.

2. Rabbit: Rabbits are also primary consumers as they mainly feed on plant material such as grass, leaves, and vegetables.

3. Elephant: Elephants are primary consumers because they are herbivores that primarily feed on plants, including grass, leaves, bark, and fruits.

In this chain, each organism directly consumes plants or plant-based materials, making them primary consumers in the food chain.

Let's compare the other options to see why they are not correct:

- Option 'B' - Grass, parrot, snake:
Grass is a producer, but parrots are not primary consumers. They are secondary consumers as they feed on seeds, fruits, and sometimes insects. Snakes are also not primary consumers as they are carnivores that feed on other animals, including birds and rodents.

- Option 'C' - Snake, hawk, tiger:
Snakes are not primary consumers as mentioned earlier. Hawks are secondary consumers as they prey on small mammals and birds. Tigers are tertiary consumers as they are top predators that feed on herbivores and other carnivores.

- Option 'D' - Bacteria, fungi, viruses:
Bacteria, fungi, and viruses are not considered primary consumers as they are decomposers or pathogens that break down organic matter or cause diseases. They do not directly consume producers.

In summary, the chain that contains primary consumers is option 'A' - Bird, rabbit, elephant.