Hello!
"Assist" means to help someone with something. Sharing part of their work. It also means to help by providing money, information, service, etc.
Here's an example sentence that uses "assist":
I worked very, very hard to assist your son and daughter.
Synonyms for "assist":
Aid, accommodate, helping hand, serve, comfort, support.
Answer: A. “Greater fuel efficiency reduces the greenhouse gases implicated in climate change.”
Explanation:
The key finding of the article was that greater fuel efficiency can help in efforts to mitigate climate change.
It showed that a greater fuel efficiency such as from a car that gets 50 miles per gallon, emitted about half the greenhouse gasses that a car that got about 25 miles per gallon.
As these greenhouse gasses are implicated in the causes of climate change, reducing their emission would help in the fight against climate change.