2018-2019人教新目标高中英语选修六课件:Unit 4 Period 3
2018-2019人教新目标高中英语选修六课件:Unit 4 Period 3第4页

②__ ____ a scientist called Charles Keeling, ____ made accurate measurements of the amount of carbon dioxide in the atmosphere. ③__ __ the burning of more and more fossil fuels ____ has resulted in this increase in carbon dioxide.

It

was

who

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is

that