单项选择题

The sharp rise of the snow geese population is mainly caused by______.

A．lack of natural enemies
B．great care of wildlife preservationists
C．favorable conditions in their winter habitat
D．changes in their migration patterns
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单项选择题
The author seems to imply that ______.
A．humans are responsible for the problem
B．hunting limits and regulations should be lifted
C．the birds have a strong capability to survive
D．the Canada geese are a better species than the snow geese
单项选择题
On which of the following assumptions is based the belief, that tree-ring thicknesses show links between solar periodicity and terrestrial climate
A．Solar-activity cycle existed m its present form during the period in question.
B．Average tree-ring thickness varies from species to species.
C．Tree-ring thickness varies with changes in terrestrial climate.
D．Both terrestrial climate and solar-activity cycle randomly affect tree-ring thickness.
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