Question 19 is based on the recording you have just heard.

        The partial skeletons of more than 20 dinosaurs and scattered bones of about 300 more have been discovered in Utah and Colorado at what is now the Dinosaur National Monument. (19) [Many of the best specimens may be seen today at museums of natural history in the larger cities of the United States and Canada.] This dinosaur pit is the largest and best preserved deposit of dinosaurs known today. (20) [Many people get the idea from the massive bones in the pit wall that some disaster, such as a volcanic explosion or a sudden flood, killed a whole herd of dinosaurs in this area. ]This could have happened, but it probably did not.

        The main reasons for thinking otherwise are the scattered bones and the thickness of the deposit. In other deposits where the animals were thought to have died together, the skeletons were usually complete and often all the bones were in their proper places. Rounded pieces of fossil bone have been found here. These fragments got their smooth, round shape by rolling along the stream bottom. In a mass killing, the bones would have been left on the stream or lake bottom together at the same level. But in this deposit, the bones occur throughout a zone of sandstone about 12 feet thick. The mixture of swamp dwellers and dryland types also seems to indicate that the deposit is a mixture from different places.

        The pit area is a large dinosaur graveyard—not a place where they died. (21) [Most of the remains probably floated down an eastward flowing river until they were left on a shallow sandbar. ]Some of them may have come from far-away dryland areas to the west. Perhaps they drowned trying to cross a small stream, or were washed away during floods. Some of the swamp dwellers may have got stuck in the very sandbar that became their grave. Others may have floated for miles before being stranded.

        Even today, similar events take place: when floods come in the spring, sheep, cattle, and deer are often trapped by rising waters and often drown. Their dead bodies float downstream until the flood recedes, and leaves them stranded on a bar or shore where they lie, half buried in the sand, until they decay. Early travelers on the Missouri River reported that shores and bars were often lined with the decaying bodies of buffalo that had died during spring floods.

19. Where can many of the best dinosaur specimens be found in North America?（在北美哪里可以找到许多保存最完好的恐龙标本？）

解析：D。根据选项中的Along、At以及后面所跟的不同地点，推测题干可能会问某种事物的地址。录音开头指出，如今，许多保存最完好的标本可以在美国和加拿大一些大城市的自然历史博物馆里看到，D项与录音表述一致，故正确。

错项排除：录音中提到了Colorado和Dinosaur National Monument，但录音说的是犹他州和科罗拉多州是发现恐龙骨架和一些碎骨的地方，也就是现在的国立恐龙公园。由此可知，这并不是保存恐龙标本的地方，故排除A、B两项。录音中说的是自然历史博物馆位于美国和加拿大的一些大城市，而不是美国和加拿大的边界，故C项排除。