問題詳情
Passage#3 Biologists recognize how necessary wetlands are to the balance of life. First, they contain anastonishing number of producers, forming the base of a complex food web. Salt marshes alone producemore green material per hectare than the best-managed farms. Second, migratory birds need wetlands forbreeding and resting areas along their flyways. Third, a wide variety of wetlands are necessary for manyspecies of waterfowls to survive. Fourth, more wetland species are endangered or threatened than anyothers. Just one example is the whooping crane. Overhunting and loss of wetland habitat have severelyreduced the numbers of this species. Fifth, salt marshes are the nurseries and farms of the ocean. Oceanfood webs begin in salt marshes where outgoing tides carry bits of living and dead material from themarshes into the ocean. This “tidal soup” feeds many of the ocean animals. Sixth, most fish and shellfishthat people eat live in wetlands when young. Shrimp, salmon, oysters, crabs, flounders, and clams dependon the salt marshes for food and shelter. They are born in marshes and may live there for a good part oftheir lives.
【題組】41. What have caused the whooping crane to dwindle in number?
(A) Overuse of DDT on agricultural crops.
(B) Loss of wetland habitat.
(C) Overuse of pesticides.
(D) Competition among species.
參考答案
答案：B
難度：簡單0.833333
統計：A(1),B(10),C(0),D(0),E(0)