Answer:
The answer is: 
Pregunto cuál es correcto.
Step-by-step explanation:
To choose the best phrase or word that completes the sentence, it is necessary to resort to the meaning of the sentence. 
For them, semantics is used, which is a part of linguistics that studies the meaning of linguistic expressions. 
The sentences that can be formed are: 
- Pregunto una limonada. In Spanish, a person does not use "Pregunto" to request or order a lemonade. 
-Pregunto su ayuda. Here the same thing happens, a person does not use "Pregunto" to request help or to ask for something.
- Pregunto cuál es correcto. In this sentence a person is requesting information about something or the person is asking clearly that he needs an answer to something. 
- Pregunto más comida. In English, a person does not use "Pregunto" to request or order more food.