Answer:
Usted tiene LAS clases de ciencias en la tarde.
Explanation:
The noun clase in Spanish means class in English. It is feminine, so the article coming before it is: LA.
la clase
(or una clase if it is undetermined)
To make it plural, we add an -s to the noun and also to the article.
clase + s = clases
la + s = las
las clases
In this example, we have the determined article before the noun clases because it is a determined kind of class: clases de ciencias (science classes).
