Question

select the simple subject. her best friend moved away last summer.

Explanation:

The simple subject is the main noun or pronoun in a sentence that the verb acts upon. In the sentence "Her best friend moved away last summer", we analyze the components. "Her" and "best" are modifiers (possessive adjective and adjective respectively) for the noun "friend". The verb "moved" shows the action done by "friend". So we identify the simple subject by removing the modifiers and finding the core noun.

Answer:

friend