用平面在正方体上截下一个三棱锥，以原来正方体的那个顶点作为三棱锥的顶点，则该顶点在三棱锥的底面上的射影是这个三角形的（　　）

惊蛰是二十四节气之一，其含义是春雷始鸣，惊醒蛰伏地下冬眠的昆虫。实际上，①____，大地回春、天气变暖才是使它们结束冬眠、“惊而出走”的原因。惊蛰雷鸣最引人注意。现代气象科学表明，②____，是因为大地湿度渐高，促使近地面热气上升；或北上的湿热空气势力较强，活动频繁。从我国各地自然物候进程看，由于我国南北跨度大，③____，“惊蛰始雷”的说法仅与沿长江流域的气候规律相吻合。

To be an artist is not easy, but sometimes dreams can be a rich source of ________—for an artist.

    Dear Student of Star Middle School:

    As your student council president, I am writing to ask for your support to start the Count-Your-Steps walking program. Mr. Stewart Thomas, a parent of two students at Star Middle School, firstly came up with the idea. Mr. Thomas is a fan of walking and wants to encourage others to appreciate the activity. He shared his idea with our principal, Ms. Howser, who immediately agreed that we should try it.

    Ms. Howser contacted the other middle schools in the district, and all the teachers eagerly adopted the program. Now a team of Count-Your-Steps organizers made up of representatives from the middle schools, has established the program's goal: to increase awareness of the benefits of walking. Organizers want middle school students to accept this challenge and make walking one of their daily activities.

    The program has clear guidelines. Interested participants must only commit to recording the number of steps taken daily. Ms. Earley, the assistant principal, will give each of us a log for recording our steps and a pedometer, which is a small, digital tool used to count the steps of the person wearing it. All participants need to do each day is to wear the pedometer, walk as much as possible, and then record the number of steps in our logs. Clearly, the process is simple and convenient.

    While the benefits of walking are multiple, this challenge offers all who participate the opportunity to work together, achieve success, and make positive changes. Remember that the other schools in the district are signed up for the Count-Your-Steps too, and each one will try to take more steps than our school. I hope many will agree to this challenge and show everyone the Star Middle School Cougar Spirit.

    Please take into careful consideration this valuable and well-planned program, and then sign up today! In the words of Mr. Thomas, “Together we can enjoy the advantages of walking.”

    Sincerely,

    Cora Jeffries