The correct answer is option 'C', Valmiki National Park.

Explanation:
Valmiki National Park, located in the West Champaran district of Bihar, was the first Tiger Reserve in Bihar. It was established in 1990 and covers an area of approximately 899.38 square kilometers.

Let's explore the reasons why Valmiki National Park is the correct answer:

1. Introduction to Valmiki National Park:
- Valmiki National Park is a protected area and a national park in Bihar, India.
- It is named after the famous sage Valmiki, who is believed to have written the epic Ramayana.
- The park is situated in the Indo-Gangetic plains, close to the Nepal border.

2. Establishment as a Tiger Reserve:
- Valmiki National Park was declared a Tiger Reserve in 1990.
- It was the first Tiger Reserve to be established in Bihar.

3. Flora and Fauna:
- Valmiki National Park is known for its rich biodiversity and diverse range of flora and fauna.
- The park is home to several endangered species, including the Bengal tiger, Indian rhinoceros, Asian elephant, and Indian python.
- It also houses a variety of plant species, including Sal, Asan, Semal, and Bamboo.

4. Conservation Efforts:
- As a Tiger Reserve, Valmiki National Park plays a crucial role in the conservation of the endangered Bengal tiger.
- The park implements various measures to protect and preserve the tiger population, including habitat management, anti-poaching patrols, and community engagement.

5. Other Wildlife Sanctuaries in Bihar:
- While Valmiki National Park was the first Tiger Reserve in Bihar, the state is also home to other wildlife sanctuaries.
- Some notable wildlife sanctuaries in Bihar include Bhimbandh Wildlife Sanctuary, Kaimur Wildlife Sanctuary, and Pant Wildlife Sanctuary.
- However, none of these sanctuaries were the first Tiger Reserve in Bihar.

In conclusion, Valmiki National Park in Bihar was the first Tiger Reserve established in the state. It is renowned for its biodiversity and conservation efforts, making it an important wildlife destination in India.