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

We celebrated Earth Day in my city last week. The idea of this special day began in the 1960s when life was very different. Few people talked or even thought about the environment. Most people had no idea how dirty our air and water were. This attitude bothered Gaylord Nelson, who was a senator in the US government, and he had an idea. If people around the world knew that the planet was in danger, they might work harder to save it, so he just needed to get their attention. The first Earth Day was just in the United States but it led to events every year all around the world on April 22 or the nearest weekend, depending on where you are.

In my town, last Saturday afternoon lots of people rode their bikes from the park, around the town together and back to the park, taking as much time as they possibly could, so that the cars had to wait. Then we talked to all the drivers in cars which just had one person in them, to explain how wasteful that is and how much pollution it causes. The idea was to make people think about how much they use their cars. In other places, people collected plastic bags for a week and then made a pile of them in the town square. You can do anything as long as it makes people of all ages come together for a few hours and talk about the environment. Last year we had a big music event for young people. Some people said it was a waste of time, but there was information for people to read and announcements between the bands about how to help protect the environment.

According to the passage, Earth Day began because ____ .