2019年全国统一考试（天津卷）英语独家解析(23)

46. What have scientists discovered with the help of mathematical models of food webs?
A. The living habits of species in food webs.
B. The rules governing food webs of the ecosystems.
C. The approaches to studying the species in the ecosystems.
D. The differences between weak and strong links in food webs.
47. A strong link is found between two species when a predator ________.
A. has a wide food choice
B. can easily find new prey
C. sticks to one prey species
D. can quickly move to another place
48. What will happen if the populations of top predators in a food web greatly decline?
A. The prey species they directly attack will die out.
B. The species they indirectly attack will turn into top predators.
C. The living environment of other species will remain unchanged.
D. The populations of other species will experience unexpected changes.
49. What conclusion can be drawn from the examples in Paragraph 4?
A. Uncontrolled human activities greatly upset ecosystems.