单项选择题

Directions: You will hear three pieces of recorded material. Before listening to each one, you will have time to read the questions related to it. While listening, answer each question by choosing A, B, C or D. After listening, you will have time to check your answers. You will hear each piece only once. Questions 11—13 are based on a report about children’s healthy development. You now have 15 seconds to read Questions 11—13. According to the report, children’s bedrooms should ______.