[托福-阅读] The Pace of Evolutionary Change tpo30-1-11

The question about the rate of evolution must now be turned around: does evolution ever proceed gradually, or does it always occur in short bursts? Detailed field studies of thick rock formations containing fossils provide the best potential tests of the competing theories.

Occasionally, a sequence of fossil-rich layers of rock permits a comprehensive look at one type of organism over a long period of time. For example, Peter Sheldon's studies of trilobites, a now extinct marine animal with a segmented body, offer a detailed glimpse into three million years of evolution in one marine environment. In that study, each of eight different trilobite species was observed to undergo a gradual change in the number of segments-typically an increase of one or two segments over the whole time interval. No significant discontinuities were observed, leading Sheldon to conclude that environmental conditions were quite stable during the period he examined.

---

Question 11 of 13

The main purpose of paragraph 7 is to

A. describe one test of the competing theories

B. provide an example of punctuated equilibrium

C. describe how segmented animals evidence both competing theories

D. explain why trilobites became extinct

告訴大家個小技巧，他問這段的目的除了可以看完整段外，可以先去上一段結尾看，因為段落間都會有點小關聯，否則就是一篇不好的文章，所以依此往上段最後一句話看"Detailed field studies of thick rock formations containing fossils provide the best potential tests of the competing theories."
所以我們得知他下一段必會介紹一個test，就是問題要我們看的那段，答案自然是a