C. forests
The sentence talks about a special ecosystem, and "forests" is the most suitable word to describe a large area of land covered with trees.
D. wildlife
The context suggests that the boat trip is to view animals living in their natural environment. "Wildlife" refers to wild animals.
A. inhabitants
"Inhabitants" refers to the people who live in a particular place. In this case, it refers to the people living in Kim Lan Village.
C. opportunities
"Opportunities" means a chance or possibility to do something. In this context, it refers to the chance to see various bird life and other animals.
D. species
"Species" refers to a group of living organisms that are similar and can breed with each other. The Siamese Crocodile is mentioned as an endangered species.