①There is no doubt that the earth is becoming warmer and that it is human activity that has caused this global warming rather than a random but natural phenomenon.
②It was a scientist called Charles Keeling who made accurate measurements of the amount of carbon dioxide in the atmosphere from 1957 to 1997.
③They also agree that it is the burning of more and more fossil fuels that has resulted in this increase in carbon dioxide.
探究发现
(1)强调句型的结构是：It_is/was＋被强调部分＋that＋句子的其他成分，如例句①、③。
(2)当被强调部分是人时，也可用who，如例句②。
