A、B两辆汽车在笔直的公路上同向行驶，当B车在A车前84 m处时，B_爱下问搜题

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问题计算题

A、B两辆汽车在笔直的公路上同向行驶，当B车在A车前84 m处时，B车速度为4 m/s，且正以2 m/s²的加速度做匀加速运动，经过一段时间后，B车的加速度突然变为零。A车一直以20 m/s的速度做匀速运动。经过12 s后两车相遇。问B车加速行驶的时间是多少？

答案

解：设A车的速度为v_A，B车加速行驶时间为t，两车在t₀时相遇。则有：x_A=v_At₀ ①

②

式中，t₀=12 s，x_A、x_B分别为A、B两车相遇前行驶的路程，依题意有x_A=x_B+x ③，式中x=84 m

由①②③式得 ④

代入题给数据v_A=20 m/s，v_B=4 m/s，a=2 m/s²

有t²-24t+108=0 ⑤

解得t₁=6 s，t₂=18 s ⑥

t₂=18 s不符合题意，舍去。因此，B车加速行驶的时间为6 s

完形填空

When growing up, I hadn't the slightest curiosity about the authors of books I read; it was the _     that was important. My mother, and sometimes my father. read _     to us every night.   I could hardly wait       I could read and write my own books. But in the first grade,
I would sit with a group of      while the teacher turned over large sheets of paper.        had been written in crayon and seemed to have something to do with       in one corner-a cat or dog or a tree in autumn. One by one the other children read aloud those black       while I sat unhappy. One day I decided that perhaps      was just making stories up. So the next time when the teacher      to the words, I eagerly _     a story about a dog attacking a cat         a tree in autumn. The teacher looked sad and-shook her _      , and I knew that I still had not discovered the magic secret.
By the time I         fifth grade, "writing books" was still my favorite hobby. I rushed home from school each day to write down       had been forming in my head. At sixteen my first story was       in a church magazine. In college, where I was studying to be a psychologist, was able to pay my       by writing stories. When I got my bachelor's degree, I decided to write more than anything else, so I began writing       . I have since published books for both children and       _ . I'm not happy unless I spend some time writing. Usually I write about six hours each day. I spend three months to a year on a children's book.         how well I know the       before I begin. A neovel for adults takes a year or two. When my work is going well. I wake early in the mornings, hoping it is time to get up.

A．figuring out

B．carrying on

C．depending on

D．bringing out

单项选择题

哪种肾脏疾病易引起高钾血症

A．急性肾衰竭(少尿型)

B．Ⅱ型肾小管酸中毒

C．Ⅰ型肾小管酸中毒

D．肾病综合征

E．巴特综合征