卫板的前端应紧贴轧辊，卫板的上表面应比孔型槽底（）。

菱形不具有的性质是        [ ]

A. 对边平行        

B. 对角相等    

C. 对角线互相平分  

D. 对角线相等且互相垂直

下表是探究绿豆种子萌发所需外界条件的实验设计，如果还要探究绿豆种子萌发是否需要光，还需设置5号瓶，对5号瓶的处理是

	1号瓶	2号瓶	3号瓶	4号瓶
处理方式	洒入少量清水，使餐巾纸湿润，然后拧紧瓶盖	不洒水，拧紧瓶盖	倒入较多清水，使种子淹没，然后拧紧瓶盖	洒入少量清水，使餐巾纸湿润，然后拧紧瓶盖
放置环境	25℃、有光	25℃、有光	25℃、有光	4℃、有光
实验结果	种子萌发	种子不萌发	种子不萌发	种子不萌发

A.5号瓶应放置在无光的环境中，其他处理与1号瓶相同

B.5号瓶应放置在无光的环境中，其他处理与2号瓶相同

C.5号瓶应放置在无光的环境中，其他处理与3号瓶相同

D.5号瓶应放置在无光的环境中，其他处理与4号瓶相同

下列离子符号书写正确的是

A．Ca⁺²

B．NH₃⁺

C．S^2-

D．Fe^2-

男性，60岁，因心前区反复发作性疼痛2年就诊。

患者经治疗以后，心源性休克纠正。半年后突然心脏骤停死亡。其最可能的原因是（）.

A.室颤

B.脑栓塞

C.心脏破裂

D. * * 肌断裂

E.室间隔穿孔

The Theory of Continental Drift has had a long and turbulent history since it was first proposed by Alfred Wegener in 1910. (46) Vigorously challenged yet widely ignored, the theory had languished for half a century, primarily due to its lack of a plausible mechanism to support the proposed drift. With the discovery of sea-floor spreading in the late 1950’s and early 60’s, the idea was reinvigorated. Plate tectonics is now almost universally accepted. Many details of the mechanism are to be worked out.

The surface of the Earth is divided into approximately six large plates, plus a number of smaller ones. The plates are’ bounded by an interconnected network of ridges, transform faults, and trenches. Ridges, also called spreading centers, occur where two plates are moving away from each Other. As the plates separate, hot molten mantle material flows up to fill the void. (47) The increased heat resulting from this flow reduces the density of the plates, causing them to float higher, thus elevating the boundaries by many thousands of feet above the colder surrounding sea floor. (48) Ridges on the ocean floor form the longest continuous ranges of mountains on the planet, but. only in a very few places on the Earth do these mountains rise above the ocean surface.

New sea floor is constantly being created along spreading centers. Obviously somewhere else old sea floor must be going away. This occurs in trenches, also called subduction zones. Trenches occur along the boundary between two plates that are moving towards each other. (49) Where this occurs, one plate is bent downwards at about a 400 angle and plunges under the other plate’s leading edge, eventually to melt back into the liquid mantle below. As the subducting plate is heated back up to mantle temperatures, certain minerals in the plate melt sooner than others. (50) Minerals that melt at lower temperatures and are lighter than the surrounding material tend to rise, melting their way up through the overriding plate to erupt as volcanoes on the ocean floor. As these volcanoes grow, they rise above the ocean surface to form lines of islands along the leading edge of the overriding plate. Numerous islands of Micronesia and Melanesia in the western Pacific were created in this way.

(49) Where this occurs, one plate is bent downwards at about a 400 angle and plunges under the other plate’s leading edge, eventually to melt back into the liquid mantle below.