单项选择题
Questions 4 to 7 are based on the following conversation. At the end of the conversation, you will be given 20 seconds to answer the questions.Now, listen to the conversation.
What is the main purpose of the research（）
A．To make preparations for a new publication.
B．To learn how couples spend their weekends.
C．To know how housework is shared.
D．To investigate what people do at the weekend.