问题 选择题

某同学为判断A、B、C三种金属的活动性顺序,设计了下列两个实验:

①将金属A放入B  的盐溶液中,看能否置换出B;

②将金属B放入C的盐溶液中,看能否置换出C.

当通过①、②中的现象仍无法判断出三种金属的活动性顺序时,还需要补做的一个实验是(  )

A.将金属C放入A的盐溶液中,看能否置换出A

B.将金属B放入酸溶液中,看能否置换出酸中的氢

C.将金属A放入酸溶液中,看能否置换出酸中的氢

D.将金属C放入酸溶液中,看能否置换出酸中的氢

答案

①将金属A放入B  的盐溶液中,看能否置换出B;可以排出A和B的活动性顺序;②将金属B放入C的盐溶液中,看能否置换出C,可以排出B和C的金属活动性顺序,所以还需要排出A和C的金属活动性顺序,所以将金属C放入A的盐溶液中,看能否置换出A,就能排出A和C的顺序.

故选A.

阅读理解
单项选择题

Generally,in order to be preserved in the fossil record, organisms must possess hard body parts such as shells or bones.Soft,fleshy structures are quickly destroyed by predators pr decayed by bacteria. Even hard parts left on the surface for and length of time will be destroyed Therefore, organisms must be buried rapidly to escape destruction by the elements and to be protected (5) agents of weathering and erosion Marine organisms thus are better candidates for fossilization than those living on the land because the ocean is typically the site of sedimentation, whereas the land is largely the site of erosion.The beds of ancient lakes were also excellent sites for rapid burial of skeletal remains of freshwater organisms and skeletons of other animals, including those of early humans Ancient (10)swamps were particularly plentiful with prolific growths of vegetation, which fossilized in abundance.Many animals became trapped in bogs overgrown by vegetation.The environment of the swamps kept bacterial decay to a minimum, which greatly (aide(D)in the preservation of plants and animals.The rapidly accumulating sediments in flood plains, deltas, and stream channels buried freshwater organisms,along with other plants and animals that happened to fall into the (15) water. Only a small fraction of all the organisms that have ever lived are preserved as fossils.Normally, the remains of a plant or animal are completely destroyed through predation and decay.Although it seems that fossilization is common for some organisms, for others it is almost impossible. For the most part, the remains of organisms are recycled in the earth, which is fortunate because (20) otherwise soil and water would soon become depieted of essential nutrients. Also, most of the fossils exposed on Earth’s surface are destroyed by weathering processes.This makes for an incomplete fossil record with poor or no representation of certain species.The best fossils are those composed of unaltered remains. Generally, it is the inorganic hard parts, composed mostly of calcium carbonate, that form the vast majority of unaltered fossils.Calcite and (25) aragonite also contributed to a substantial number of fossils of certain organisms.

The fact that the "land is largely the site of erosion" (line 7) is significant because ().

A.erosion is less destructive than sedimentation

B.fossils are most common in areas Subject to erosion

C.erosion contributes to the destruction of skeletal remains

D.few organisms live in areas that experience extensive erosion