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 questions from 34 to 40.

Although there is not a simple answer, scientists and environmentalists are developing new ideas to address the plastic problem. Some scientists are working on developing biodegradable replacements for plastics. A group of researchers from Harvard created a plastic-like substance made from shrimp shells. In Indonesia, a company replaced plastic bags and soap wrappers with packaging made from seaweed.

Instead of engineering plastic replacements, others are taking on the collection of plastics in landfills and oceans. Microbiologists from Pakistan tried using mushroom enzymes to break down plastics in garbage dumps more quickly. Engineers in the Netherlands developed a nearly 2,000-foot-long ocean garbage truck, which travels the waters and collects plastics. Known as System 001, this ocean trash collector is heading to the Great Pacific Garbage Patch for some cleanup. A nonprofit organization called The Plastic Bank pays community members for plastics that they collect. By incentivising plastic pick-ups, The Plastic Bank prevents these materials from ending up in the ocean and recycles the collected plastics into new products. Environmentalists also recommend that citizens can take action to decrease their consumption of ever-convenient plastics. Environmentalists urge citizens to reduce their use of single-use plastics, plastics used once and then tossed. Worldwide, 73% of beach litter comes from single-use plastics, like plastic straws, cups, bags, and utensils, reports National Geographic.

Secondly, environmentalists encourage individuals to recycle plastics. Recycled plastics can be repurposed into new products - suitcases, furniture, new bottles, laundry detergent, and much more. But it is important to sort recyclables from trash carefully. Tom Szaky, CEO of a recycling company, said, "Typically, 50% of what you put in your recycling bin is never recycled. It's sorted and thrown out. This is partly due to user error, a common problem which occurs when people place unrecyclable materials into recycling bins."

What does the word they in paragraph 2 refer to? A. Participants who had no social media limits B. All social media users C. Participants who limited their time on social media D. Researc