设其导函数在x=0处连续，则λ的取值范围是（）。

阅读下面文字，依次概括无舵雪橇比赛过程的四个关键步骤，每个步骤不超过8个字。（4分）

无舵雪橇是冬季奥运会比赛项目之一。比赛开始时运动员坐在雪橇上，双手借助起点助栏用力向后推，使雪橇向前起动。滑行中仰卧在雪橇上，单手拉住雪橇皮带利用身体起卧，变换肩，腿姿势操纵雪橇，使之沿着冰道快速滑降。其间选手可选择最理想的线路前进，以尽可能地减少比赛用时。到达终点时，运动员须坐在雪橇上，否则不予计算成绩。

下列结构中含叶绿体较多的是[ ]

A．海绵层

B．栅栏层

C．叶脉

D．表皮

互斥方案比选时，用净现值法和增量内部收益率法进行项目比选的结论( )。

A．相同

B．不相同

C．不一定相同

D．近似

Did you ever have someone’s name on the tip of your tongue and yet you were unable to recall it (1) this happens again, do no (2) to recall it. Do something (3) for a couple of minutes, (4) the name may come into your head. The name is there since you have met (5) person and his name. It (6) has to be dug out. The initial effort to recall (7) the mind for operation, but it is the subconscious (8) that go to work to dig up a (9) memory. Forcing yourself to recall (10) never helps because it doesn’t (11) your memory；it only tightens it. Students find the preparatory method help (12) examinations. They read over the questions (13) trying to answer any of them. (14) they answer first the ones (15) which they are most confident. Meanwhile, deeper mental activities in the subconscious mind are taking (16) ; work is being done on the (17) difficult questions. By the time the easier questions are answered, answers (18) the more difficult ones will usually begin to (19) into consciousness. It is often (20) a question of waiting for recall to come to the memory.

7（）

A.leads

B.begins

C.helps

D.prepares

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