Subjunctive mood is used to express wishes and possibilities, whereas on the other hand, indicative mood is used for facts. So let's go through all of these sentences:
1. I would go for a walk if it weren't raining - this is subjunctive. The form <em>weren't </em>used as a possibility is indicative of subjunctive mood. This person <em>wishes </em>he could go for a walk, but cannot because it is raining
2. I wish you continued at your job - this is also subjunctive. The form <em>continued is </em>is indicative of subjunctive mood. This person <em>wishes </em>something happened, but it didn't.
3. Brett wants Molly and Trent to study with him. - this is indicative. It is a fact that this person wants, so this is not subjunctive.
4. Coach recommends that we run two laps around the track. - this is subjunctive. The coach <em>wishes </em>something would happen - he is going to make his students to what he wishes them to do.
With verbs such as recommend, wish, suggest, demand, etc., subjunctive mood is used.
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! :)
