Answer:
Most of the time grammar comes after 'common sense" which is inevitable. Grammar rules don't matter anymore when it comes to informal conversation. We only pinpoint grammar errors when we don't understand the statement. So the easiest way to know if the sentence makes sense is to check if in all time subject agrees to its predicate or supporting details.
Explanation:
Hoy es Lunes
2 correcto
3...im not very sure, but , cómo will be my answer
4cuantos estudiantes hay en la sala?