题目

参数方程的曲线是(    )A.圆             B.双曲线           C.椭圆(无左顶点)        D.椭圆(无下顶点) 答案：解析：由t∈R,令t=tanφ,φ∈(-,)，则由三角万能公式，得2φ∈(-π,π).这是椭圆的参数方程，且y≠-1, 因此曲线是没有下顶点的椭圆，选D.答案:D Although in 1947 we were still very new to the atomic age, we knew about mushroom clouds． A huge crack spread across the library wall upstairs, sending teachers and students screaming down the hall．Had a new world war started? Pale-faced, our young science teacher quickly organized us for a fire drill． We huddled in little groups on the beach side of the school grounds and watched the spreading cloud darken the bright spring sky．Rumors flew every which way, although two hours would pass before we got the full story．One rumor we heard was that the Texas City Monsanto Chemical plant had blown up; children whose parents worked there began to weep．I froze—that was where my father was working that day．The school bell called us back inside, and we were dismissed to find our way home the best way we could． I-d walked a quarter of the three-mile trip to my home when a car horn startled me to attention． My Uncle Barney pulled up alongside me in his old Ford． The instant I saw him, I knew my father was gone． Otherwise, Papa would have come for me himself．As if in slow motion from a great distance, Uncle Barney motioned for me to get in． Numb with grief, I crawled into the back seat． I barely took notice of the man sitting there, and didn’t recognize him until he reached for me． When Papa put his strong arms around me, I forgot for a moment that Cherokees（柴罗基人） aren’t supposed to cry．Many of my fellow students lost their parents in the explosion． Tragedy would one day come to our family, as it inevitably comes to all, but on the day Texas City blew up, it miraculously passed us by． Because he lost his keys on that April morning, as he explained, my father lived for another 32 years-we were to have a second lifetime forever．【1】 What happened according to the first three paragraphs?A． A war broke out． B． An earthquake happened．C． An atomic bomb exploded． D． A chemical factory blew up．【2】 How did the science teacher react to the accident?A． He was sad． B． He acted quickly．C． He panicked． D． He felt helpless．【3】Which of the following statements is TRUE?A． The author-s father didn-t have to work that day．B． The author-s father had a narrow escape．C． The school was near where the accident happened．D． The author-s uncle broke the news of her father-s death．【4】The author cried because ．A． she was grateful that her father had survivedB． her father was killed in the accidentC． she was sad over the tragedy that dayD． her father didn’t meet her after school【5】 What does the author intend to tell us?A． Be prepared for the worst．B． Be brave in disasters．C． Cherish everything that you have．D． Parents are the most important people．