Their are three types of infinitives. 
        
             
        
        
        
The verb estar is an irregular verb, that means, it does not follow the pattern of all other "regular" -AR verbs.  
The verb estar means "To Be" for temporary characteristics.
Think LCP (Large Cheese Pizza)
L- Location
C- Condition
P- Participle.
Those are when you use estar.
Conjugations of estar:
I am yo estoy
you are(Informal) tu estás
he/she is / you are(Formal) el/ella está // ud. está
We are nosotros estamos
You all are (spain only) - Vosotros Estáis
They are Ellos/Ellas/Uds. Estan
Sentence: I am happy today
Yo estoy feliz hoy
 
        
             
        
        
        
Estamos: we are
estas: you are
estan: they are
The question says where are Maria and Adela? You should change “Maria and Adela” to they, do the third option is correct.
        
                    
             
        
        
        
Answer:
1. es
2. estan (with accent on a)
Explanation:
It gives the sentence proper meaning
La senora Vila es... 
Sus sobrinos no estan... 
 
        
             
        
        
        
Answer:
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Translation: <u>It's</u><u> </u><u>eleven</u><u> </u><u>fifteen</u><u> </u><u>at</u><u> </u><u>night</u><u>.</u>