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! :)
Answer:
Although students may feel they have too much homework, a study found that today's students have the same amount as their parents did.
Explanation:
B.) "She's gone from sounding like the smoke detector"
B, if you only study for a few minutes in each subject each night you have the chance to review what you studied the night before