以下关于速度和加速度的说法正确的是( ) A.速度减小时,加速一定也减小 B.加

题型:选择题

问题:

以下关于速度和加速度的说法正确的是(  )

A.速度减小时,加速一定也减小

B.加速度减小时,速度一定也减小

C.速度增加时,加速度也可能减小

D.加速度不变时,速度也不变

考点:加速度
题型:选择题

蔬菜中有机磷农药残留过多,容易引起有机磷中毒,患者表现为肌肉震颤不止,严重者会死亡。原因是有机磷农药能抑制乙酰胆碱酯酶的活性,抑制乙酰胆碱(兴奋性递质)的分解。

(1)有机磷农药作用的结构是突触,此结构中兴奋传递的信号转换是电信号→________→__________。

(2)如刺激蛙的神经纤维,该处膜内外的电位情况是____________。

(3)请你利用下列实验材料来验证有机磷农药的毒害作用。

实验材料:两个临时剥制的相同青蛙神经—肌肉标本,放电装置,有机磷农药,两个培养皿,生理盐水等。

实验步骤:

①.取两个培养皿,编号1、2,加入等量的生理盐水,分别将青蛙的神经—肌肉标本浸泡在生理盐水中。

②.用电刺激神经—肌肉标本,肌肉组织兴奋收缩,并及时舒张。

③.在1号培养皿中滴加适量的___________,2号培养皿中滴加_______________。

④.一段时间后,同时给两个神经—肌肉标本施加适当的电刺激。观察标本的情况,1号表现为______,2号表现为_________。

实验结论:有机磷农药中毒能使肌肉震颤不止。

题型:选择题

一个梯形的上底和下底的和是40dm,高是18dm,它的面积是______dm2,用两个这样的梯形拼成的平行四边形的面积是______dm2

题型:选择题

任务型阅读:  下面的五个人都想找房子,以下各题是他们的个人情况介绍.阅读所给出的六则广告简介(A---F).选出符合个人需要的最佳选项.选项中有一项是多余的.

__小题1:Mr. and Mrs. Robinson have four children. They haven't got a car, so they want to live downtown. They can pay $500 a month, but they can't pay more than that.

小题2:Mr. Smith has been retired and he is alone. He is now not in good health. He wants a house in the country which is very quiet and near to see the doctor.

__小题3:The Williams are very rich, and they want to find a clean and comfortable house. They have a lot of friends and often invite them to spend the weekend in their house.

__小题4: Mrs. White has a young daughter who is only seven years old, but she doesn't want to spend too much time sending her child to school. And she also likes a house near a park or the forest.

__小题5: Mr. Jackson is a truck driver and he has two children, one of whom has a car and is going to get married. So they want to find a house where they can park their car and truck easily.

A:  A small house in the country, two miles from a village but near a hospital,  450 dollars a month. Call 821-7146 for an evening or Sunday appointment.

B:  Now available at Franklin Park, one block from a primary school. Two bedrooms at $225. Utilities included except electricity. One month's deposit(押金)required.

C:  A flat of 120 square meters, with three bedrooms, a bathroom and a kitchen is in a building on New Street, which is not far from the center of the city. In each bedroom there is a bed, a sofa, a desk and two chairs. The rent is $480 per month. Five or six buses take you straight to the school, the hospital, the supermarket, and the train station.

D:  Nice modern apartment with nine bedrooms, a swimming pool and lovely gardens, start Jan. 1, partly furnished, with water and dryer, central air conditioning, 1800 dollars a month.

E:  A house available for rent-furnished. Street Croix, Virgin, pool, wide ocean view. No buses but a parking lot nearby, $200 weekly. November--April. SR Box Y---680.

题型:选择题

以下关于图的说法正确的是______。
Ⅰ.在一个有向图的拓扑序列中,若顶点a在顶点b之前,则图中必有一条弧<a,b>
Ⅱ.若一个有向图的邻接矩阵中对角线以下元素均为0,则该图的拓扑序列必定存在
Ⅲ.在AOE网中一定只有一条关键路径

A.Ⅰ、Ⅱ
B.Ⅱ、Ⅲ
C.Ⅰ、Ⅲ
D.仅有Ⅱ

题型:选择题

矿井通风方式有()类型

A、分区中央式

B、中央式

C、对角式

D、分区对角式

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