Read the answer explanations

A. The correct answer is 3 ("that" refers to the noun "fossil fuels"; "as" forms the phrase "as well as").

B. The correct answer is 6 ("looking form" completes the Present Continuous tense form of the verb "to look for").

C. The correct answer is 7 (the participle "leading" follows "the planet will become too hot").

D. The correct answer is 1 ("that" follows the ideas "help reduce carbon dioxide emissions and create machines and appliances" and adds more information).

E. The correct answer is 2 ("thus" is used to give information about what will happpen as a result of using biodegradable products).

F. The correct answer is 5 ("which" follows "co-workers can carpool" and is used to give extra information about it).