读图，地球公转示意图，今天（6月20日），地球位于图中的哪个位置附近（    ）

如图所示，三个共点力F₁、F₂与F₃作用在同一个质点上，其中，F₁与F₂共线且反向，F₃与F₁垂直，F₁=6N、F₂=2N、F₃=3N。则质点所受的合力为（   ）

为探究某些生态因素在生态系统中的作用，有人设计了如下实验：

①在四个大小形状相同的瓶中加入等量的清水，另外向C、D瓶中加入等量的相同河泥．

②向B、C、D中放入等量的生长状况相近的绿色植物水草

③向四个瓶中放入大小形状和生长状况相近的小鱼各两条．

④把A、B、C瓶置于阳光下，D瓶放在黑暗的环境中．

实验装置如图所示，请分析回答下列问题：

C

    Next week is Family Learning Week and there will be many activities (活动) at schools in the city.

    There is a very interesting art class at Hadley School. Its name is "Paint with your parents". It's on Saturday, October 28th. It is for anyone with children under 16. It's a two-hour class it begins at 9:15 in the morning

    An interesting thing about this class is one of the teachers, a famous writer. Her name is J.P. Hayward She will read from her new book. Listening to her will give you ideas to use in your paintings.

    A family ticket (票) is $8. That's for four people. Anyone extra (额外的) has to pay (付费) $3.

    If you are interested in this class, please call Mr. Henry. The phone number is 456-3290. I hope you all enjoy Family Learning Week.

根据材料内容选择最佳答案。