下列关于相关反应的叙述错误的是（　　）

已知实数x，y满足条件$\{\begin{array}{c}y\le 0\\ y\ge x\\ 2x+y+4\ge 0\end{array}$，则z=x+3y的最小值是（   ）

B

    “Mum, may Patti come over?” asked Meg.

    “Not until you clean your room,” replied Mum.

    Meg said on the phone unhappily, “I have to clean my room first.”

    At the other end, Patti laughed. She said to Meg, “That's funny. My mum just said I can't go anywhere until I clean my room.”

    After hanging up (挂断电话), the girls went to their own rooms. Each girl looked around at her mess. Slowly they started cleaning their rooms.

    Meg said to herself, “Maybe we could talk on the phone while we work. It would be hard to work and talk at the same time, though.”

    Patti thought, “Until I clean my room, I can't leave. Meg may leave, but she can't have anyone over.” Then Patti asked her mum, “Mum, may Meg come?” “Sure,” said Patti's mum. “Remember, you must have your room cleaned before leaving the house.”

    Patti ran to the phone and called Meg. “I've got an idea!” she told Meg.

    A few minutes later, Meg went over to Patti's house. Her mum allowed her to go because she promised to clean her room when she returned.

    While dancing, singing and talking, the girls worked. One hour later, the room became clean. It was fun! The room looked great. Patti's mum was happy. She called Meg's mum and told her everything. Meg's mum said Patti could come to help Meg.

    The girls quickly went to Meg's house. They worked and played until the room was clean. The girls learned that working together could make cleaning fun and easy!

    It's Sunday morning. There are many people in the park, some boys are playing basketball. There are some girls under a big tree. They're singing and dancing. What are those women doing? They are drinking tea. Look at the woman in a blue coat. Who's she? She's my mother. She is talking to Edward. Edward is her student. He is a good student. He studies hard. He's good at all the subjects. And he's friendly to all his teachers and his friends.