单项选择题

______ has warmed the waters off Alaska.

A．El Nino
B．The sun
C．Over-population
D．Pressure
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单项选择题
One reason it is difficult to know why the whales are dying is that ______.
A．the whales travel such a long distance
B．there are more whales than there used to be
C．the whale bodies are too old to study by the time they are found
D．the whales are endangered
单项选择题
About how many more whales have been sighted in the San Francisco Bay this year compared to last year
A．Twice as many.
B．Three times as many.
C．Half as many.
D．About the same.
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