The sentence hoy es lunes translates into today is monday. So this is the correct answer because when telling the day we use the formula:
Hoy + es + day of the week
So es comes from the verb ser and is used when we want to tell the day of the week.
As in the previous sentence, here we use the formula:
Hoy + es + day of the week
So the day of the week here is jueves (Thursday). So hoy es jueves means today is Thursday. The other part of the sentence el primero de junio means June first.
This sentence is incorrect because of the word as. The correct word here is es that comes from the verb ser and is its conjugation for the third person singular in the simple present. The verb ser is being used here as description, talking about the essential qualities that describe a person like the physical description.
This is a relative pronoun are because it's related to a noun that has previously been stated. We use the relative pronoun quien only to refer to people. Also, its plural form is quienes having no masculine/feminine distinction. So this question word can also have a plural form.
We can translate the word cuántos in this question as how many. Therefore, the noun that comes after this word must match the plural form. Estudiantes (students) is the plural form of estudiante (student). So this question can be translated as follows:
How many students are there in the classroom?
