Final answer:
The appropriate present tense form to fill in the blank in the sentence 'La clase de la Sra. Álvarez, _______ muy difícil.' is 'es', which is the present tense form of 'ser'. 'Ser' is used to express inherent characteristics or permanent conditions.
Step-by-step explanation:
The appropriate present tense form to fill in the blank in the sentence 'La clase de la Sra. Álvarez, _______ muy difícil.' is 'es', which is the present tense form of 'ser'.
In Spanish, 'ser' is used to express inherent characteristics or permanent conditions. Since the difficulty of the class is considered a permanent condition, 'ser' is the correct verb to use in this context.
For example, 'La clase de la Sra. Álvarez es muy difícil, pero es muy interesante.' (Mrs. Álvarez's class is very difficult, but it is very interesting.)
Learn more about the appropriate present tense form of ser or estar