31 Which of the following sentences best expresses the main idea of the first paragraph? (A) Microbeads are contaminating waterways in a harmful manner. (B) Microbeads are appearing in the tap water people use every day. (C) Microbeads are a clever design to cleanse the pores and remove surface stains from teeth. (D) Microbeads are clogging up the bathroom drains and wastewater treatment systems.