2. Scientists are trying to find cheap, clean and effective sources of energy for the future.(looking) 

⇒ Scientist are looking for cheap, clean and effective sources of energy. (trying to find=looking for)

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 3. Carbon dioxide has a negative impact on the environment. (negatively) 

⇒ Carbon dioxide impacts negatively on the environment. (adj+N = V+adv) 

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 4. Alternative sources of energy are plentiful. They are also clean and safe. (not only) 

⇒ Alternative sources of energy are not only plentiful, they are also clean and safe.

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 5. Wind and solar made up 10% of the world's electricity in 2019. (accounted) 

⇒ Wind and solar accounted for 10% of the world's electricity in 2019. (made of = accounted for) 

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