Question

Which of these described climate rather than weather?

Answer 1

The answer is:  [C]: 
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             "Annual high temperatures in the summer have increased over
 many decades."
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Note:  Refer to:  "...have increased OVER MANY DECADES..." ;  whwic indicates "climate" rather than "weather".  Note that "weather"' may change, however slightly, from "day to day".  The climate refers to longer-term, overall trends.
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Answer 2

Annual high temperatures in the summer have increased over many decades.