科学家们根据蝙蝠超声导航的原理发明了声呐,利用声呐系统可以探知海洋的深度,已知声

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问题:

科学家们根据蝙蝠超声导航的原理发明了声呐,利用声呐系统可以探知海洋的深度,已知声音在海水中的传播速度1450m/s,用声呐向海底垂直发射声波,并测得接收回声所用的时间为4s,求海底的深度.

考点:回声及回声测距离的应用物质的三态及其基本特征
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It is the year 2050 now. Tom and I want to visit the Mars. It is a planet (行星) far away from our planet---the      .

Our spaceship (太空船) flew       two weeks to get to the Mars. When we arrived, we       the door of the spaceship and looked out. The weather there      sunny and hot. We saw an alien (外星人) behind a tree.       is very tall and big and has brown hair.“Help me!”     the alien.Then we saw some monsters (怪兽)  running after       alien from the house near a tree. They wanted to kill him. So we had to run away      !We both moved to the        and jumped in. We also took the alien into our spaceship and       him. What an exciting day!

小题1:A. Moon                    B. Earth                C. Sun

小题2:A. for                     B. on                   C. in

小题3:A. closed                B. opened               C. had

小题4:A. did                   B. was                  C. isn’t

小题5:A. Him                     B. He                   C. They

小题6:A. shouted                B. talked               C. told

小题7:A. another                B. other               C. others

小题8:A. quickly                 B. easily              C. luckily

小题9:A. house                   B. spaceship            C. tree

小题10:A.scared                  B. interested           C. saved

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塑料棚可延长花卉生长期,进行()栽培。

A.促成

B.养护

C.调控

D.抑制

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台湾岛有“米仓”和“糖罐”之称的地区是

A.台东山地

B.台西平原

C.澎湖列岛

D.钓鱼岛

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朱砂在癫痫治疗中的适宜用量一般为()

A.每日0.5~1g

B.每日0.5~3g

C.每日0.5~1g,服药时间控制在1个月以内

D.每日0.5~3g,服药时间控制在1个月以内

E.每0.5~1g,服药时间控制在1年以内

题型:问答题

国家实行()管理制度。

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