Final answer:
The sentence that explains Estefanía García's need for the internet for school is option (b), which mentions her use of the internet to research school projects.
Step-by-step explanation:
The sentence that explains why Estefanía García needs the internet for school is (b) 'Estefanía García uses the internet to research school projects.' This sentence directly indicates her personal use of the Internet for educational purposes, making it clear why she finds it necessary for schoolwork. Unlike the other options which describe a general importance of the Internet or the actions of other people, option (b) specifically addresses Estefanía's own use of the Internet for her school projects.