Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions.

Tourism will always have an impact on the places visited. Sometimes the impact is good, but often it is negative. For example, if lots of people visit one place, then this can damage the environment. The question is - how can we minimize the problems without preventing people from travelling and visiting places?

The main aim of ecotourism is to reduce the negative impact that tourism has on the environment and local people. The idea is to encourage tourists to think about what they do when they visit a place.

It's great to talk about protecting the environment, but how do you actually do this? There are a number of key points. Tourists shouldn't drop litter, they should stay on the paths, they shouldn't interfere with wildlife and they should respect local customs and traditions.

Some people see ecotourism as a contradiction. They say that any tourism needs infrastructure - roads, airports and hotels. The more tourists that visit a place, the more of these are needed and, by building more of these, you can't avoid damaging the environment.

But, of course, things aren't so black and white. Living in a place of natural beauty doesn't mean that you shouldn't benefit from things like better roads. As long as the improvements benefit the local people and not just the tourists, and the local communities are consulted on plans and changes, then is there really a problem?

In 2002 the United Nations celebrated the "International Year of Ecotourism". Over the past twenty years, more and more people have started taking eco-holidays. In countries such as Ecuador, Nepal, Costa Rica and Kenya, ecotourism represents a significant proportion of the tourist industry.

What is the main idea of the passage?