It is important to study polar bears to assess the health of the ecosystem on the Arctic, because（）
A: they are on the edge of extinction.
B: they are on the top of the ecosystem.
C: the food chain on the Arctic depends on them.
D: there are no other big animals on the Arctic.
A: they are on the edge of extinction.
B: they are on the top of the ecosystem.
C: the food chain on the Arctic depends on them.
D: there are no other big animals on the Arctic.
举一反三
- If the number of polar bear reduced due to the less sea ice coverage, what will be the Arctic ecosystem impacted?[img=631x714]180331808efc09e.png[/img] A: Top down control, the seal numbers will decrease. B: Top down control, the benthos will decrease. C: Top down control, the benthos will increase D: Bottom up control, the seal will increase.
- What are the characteristics of a food chain? A: It is made up of 3 to 5 links. B: It begins with a green plant, belonging to the producer of ecosystem. C: Other links are usually predatory animals, belonging to the consumers of ecosystem D: The carrot, the corn and the trees are usually producers.
- The biggest difference of Arctic （北极）and Antarctic（南极） is A: The Arctic is the ocean surrounded by land, and the Antarctic is the land surrounded by ocean B: Arctic is bigger than Antarctic C: Arctic is warmer than Antarctic D: Upwelling is mostly at Arctic
- The Arctic fox is found throughout the Arctic, usually on tundra or mountains （）the sea. A: by which near B: near of C: because near D: near
- Shark is to hammerhead as bear is to () A: arctic B: cub C: moose D: polar E: paw