In Spanish, the verb "ser" is used to describe identity, characteristics, and professions, among other things. The correct form of "ser" to use depends on the subject of the sentence.
Option 1: "soy"
"Soy" is the first person singular form of "ser," used with "yo" (I). It would not be appropriate here because the subject is "Tú y yo" (You and I), which is plural.
Option 2: "eres"
"Eres" is the second person singular form of "ser," used with "tú" (you). It is not suitable here because the subject is plural.
Option 3: "es"
"Es" is the third person singular form of "ser," used with "él/ella/usted" (he/she/you formal). It does not fit the plural subject "Tú y yo."
Option 4: "somos"
"Somos" is the first person plural form of "ser," used with "nosotros/nosotras" (we). Since "Tú y yo" translates to "You and I," which is equivalent to "we," "somos" is the correct form to use.
Therefore, the correct sentence is: "Tú y yo somos estudiantes."