题目

在昌南大道的平直路面上行驶的无人驾驶汽车甲和乙，其x—t图像分别为图中的直线和曲线，已知乙车的加速度恒定，t = 3s时，甲车和乙车的图线恰好相切，则（） A . 甲车的速度一直在增加 B . t = 0时刻甲车和乙车的距离为13.5m C . 乙车的加速度大小为2m/s2 D . 乙车在t = 1s时刻的速度方向发生变化 答案：B Since 2017, short videos have gotten millions of views (关注) online. Many people create and share short videos on popular video apps like Douyin and Kuaishou. You can even add music and special effects (特效) to your videos. The videos are 15 seconds to a few minutes long. They show people doing activities like cooking, exercising and singing.Teenagers especially enjoy these videos. More than 50 percent of Grade 7 and 8 students said they enjoy watching these short videos. About 47 percent of them have posted their own videos, according to a recent report by the China National Youth Palace Association.The videos let teenagers see funny and exciting things they wouldn’t usually see. Many teens like to share the fun things they do with others as well. For example, a 12-year-old user named Xiao Qianyu has posted videos showing her learning jazz dance. This has won her many fans.However the videos can also cause trouble. Some students spend too much time watching them and not enough time studying. Some videos are vulgar and not suitable for teenagers.To deal with this problem, Douyin added a new function (功能). It locks the app if someone uses the app for over two hours a day. Also the government asked companies to make more strict rules for these apps and cancel the unsuitable videos.1.Kuaishou is a kind of popular__________app.A.exercising B.video C.cooking D.music2.The Chinese meaning of vulgar in Paragraph 4 means “__________” in Chinese.A.冗长的 B.健康的 C.积极的 D.低俗的3.The passage tells us that__________A.teenagers can't use the app over 2 hours a day on Kuaishou.B.a video about learning jazz dance can't be posted on Douyin.C.more than 50% of the teenagers have won many fans on the apps.D.about 47% of the students in Grade 7 and 8 had shared videos on the apps.4.Maybe the passage comes from__________.A.a history book B.a sports magazine C.a newspaper D.a science book5.If we divide the passage into three parts, which of the following is the best?(①=Para.1 ②=Para.2 ③=Para.3 ④=Para.4 ⑤=Para.5)A.①②;③④;⑤ B.①;②③;④⑤ C.①②;③;④⑤ D.①;②③④;⑤