"The food that was purchased in the lunchroom must be eaten in the classroom." What is the adjective clause?

The answer to your question here is=

"The food that was purchased in the lunchroom must be eaten in the classroom."

Explanation:

An adjective clause is a dependent clause that, like an adjective, modifies a noun or pronoun. An adjective clause begin with words such as that, when, where, who, whom, whose, which, and why.

An essential (or restrictive) adjective clause provides information that is necessary for identifying the word it modifies.

In your question, 'that' modifies the noun 'food'.

Thats all i know.Hope it helps you

B) Alexander expanded his empire, thus spreading Greek culture.

Explanation: The passage "Alexander the Great" explains the life and journey of Alexander and addresses several facts that led to his success, such as his father's participation in expanding Greek culture and his short rule. However, the statement "Alexander expanded his empire, thus spreading Greek culture." best identifies the central idea, focusing on how thanks to his conquests in quite specific political contexts, he expanded his reign.