What does the word “This” in paragraph 2 refer to?

Câu hỏi: Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions from 31 to 35.
A Plastic Ocean is a film to make you think. Think, and then act. We need to take action on our dependence on plastic. We've been producing plastic in huge quantities since the 1940s. Drink bottles, shopping bags, toiletries and even clothes are made with plastic. We live in a world full of plastic, and only a small proportion is recycled. What happens to all the rest? This is the question the film A Plastic Ocean answers. It is a documentary that looks at the impact that plastic waste has on the environment. Spoiler alert: the impact is devastating.
The film begins as a journey to film the largest animal on the planet, the blue whale. But during the journey the filmmakers (journalist Craig Leeson and environmental activist Tanya Streeter) make the shocking discovery of a huge, thick layer of plastic floating in the middle of the Indian Ocean. This prompts them to travel around the world to look at other areas that have been affected. In total, they visited 20 locations around the world during the four years it took them to make the film. The documentary premiered in 2016, and is now on streaming services such as Netflix.
It's very clear that a lot of research went into the film. There are beautiful shots of the seas and marine life. These are contrasted with scenes of polluted cities and dumps full of plastic rubbish. We see how marine species are being killed by all the plastic we are dumping in the ocean. The message about our use of plastic is painfully obvious.
But the film doesn't only present the negative side. In the second half, the filmmakers look at what we can do to reverse the tide of plastic flowing around the world. They present short-term and long-term solutions. These include avoiding plastic containers and 'single-use' plastic products as much as possible. Reuse your plastic bags and recycle as much as you can. The filmmakers also stress the need for governments to work more on recycling programmes, and look at how technology is developing that can convert plastic into fuel.
We make a staggering amount of plastic. In terms of plastic bags alone, we use five hundred billion worldwide annually. Over 300 million tons of plastic are produced every year, and at least 8 million of those are dumped into the oceans. The results are disastrous, but it isn't too late to change. Once you've seen A Plastic Ocean, you'll realise the time is now and we all have a role to play.
(Source: https://learnenglish.britishcouncil.org)
What does the word "This" in paragraph 2 refer to?
A. The discovery of plastic in the Indian Ocean.
B. The journey of following the blue whale.
C. The travel around the world.
D. The huge amount of plastic waste in the oceans.