( )是指按照既定的目标和标准，对组织活动进行监督、测量，发现偏差，采取纠正措施，

旧区改建应遵循加强维护、合理利用、调整布局、逐步改善的原则，防止大拆大建，不加区别地推倒重来，改建的重点地区应是( )。

A．危房简屋、设施简陋、街巷狭窄、住户拥挤

B．危房简屋、设施简陋、交通阻塞、污染严重

C．房屋破旧、设施不全、交通不便、污染严重

D．房屋破旧，交通阻塞、设施简陋、住房拥挤

局限性肺气肿不发生于（）

A.中央型肺癌

B.支气管异物

C.中央型错构瘤

D.肺炎

E.肺结核纤维化周围

探究的一般过程是开始于[ ]

A．作出假设  

B．发现问题、提出问题  

C．制定和实施计划  

D．表达和交流

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.

(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.