Please help!! What are some grammar rules or hunches you have about Spanish -er verbs? Write in complete sentences (in English).

Every proper sentence in Spanish must have a subject and a verb. There is also a proper place for subjects and verbs in a sentence.

Begin a sentence with the subject (the person, place, or thing you’re talking about). Follow that with the verb, and then the rest of the sentence (where, how, etc).

i would say "están" :

corras is the only one that is informal but doesn't follow the suffix rule. correr is the verb. corre is the formal verb form. corra would be used as the formal is corre ended with an a.

your best bet would be corras, it's the only one that is informal but is still wrong