Young schoolteacher Charles Edward Chipping (Robert Donat) imposes strict discipline on his young charges at a Victorian-era English public school, becoming a fearsome presence on the campus grounds. But the love of spirited young suffragette Katherine Ellis (Greer Garson) brings the Latin instructor out of his shell and makes him a beloved campus institution into the 20th century and through the shattering violence of World War I. The film is based on the best-selling novel by James Hilton.
B. She silently comforts her friend by squeezing his hand.
A, because your peers are are the people are you are friends/go to school with, and pressure will influence your behaviors
Your first option is correct.
EXPLANATION:
your first option is correct because this is a grammar question. When you use "an" you're using it in front of a vowel. The only sentence starting with a vowel is the first one. The others don't sound right when you use "an" in front of it instead of "a".
I hope I helped! :)