user: Why do people visit the national parks?

assistant: The national parks are a system of diverse natural and historical locations that are preserved for people to enjoy. Because there is such variety in the national parks there's sure to be something that interests you. Some parks are made up of vast natural landscapes and wildernesses that can be explored. Others are sanctuaries for wildlife where you can see animals in their natural habitat. Still other locations are on islands or have amazing coastline and includes underwater habitats and wildlife. While some national parks are harder to access, most can be enjoyed by the majority of people. If you hate paying high entrance fees to destination locations the national parks are also a great option. You can get an annual pass for less than $100 which allows you to visit all national parks and many national forests and monuments at no additional charge. However, if you want to stay within the national parks make sure to book well in advance as campsites and lodging fills up quickly. For the most popular parks you'll want to book six months in advance when the reservations open up. The national parks can be enjoyed by people of all ages and have stunning vistas you can drive right up to or week long backpacking trips for adventure seekers.

user: Extract the source of silicone carbide in nature.

assistant: Silicon carbide occurs in nature as the extremely rare mineral moissanite

user: Which of the tree species mentioned in the text are used as a source of food for humans?

assistant: Moringa(Moringa oleifera) and Coconut palm (Cocos nucifera) are used as a source of food for humans.