Select the most appropriate option to fill in the blank and make a grammatically correct sentence.

Robert and Rooney aren’t very good friends although they ________ each other for a long time.

have known

The most appropriate option to fill in the blank and make a grammatically correct sentence is:

☀ have known

The sentence would read: "Robert and Rooney aren’t very good friends although they have known each other for a long time."

Explanation: The present perfect tense "have known" is used here because it indicates an action that began in the past (their acquaintance) and continues into the present. The other options don't fit the context:

• Are knowing: This is not a correct form of the verb tense for this context.

• Has known: This doesn't agree with the subject "Robert and Rooney," and it's not the correct tense for the sentence.

• Knew: This is the past simple tense, but it doesn't convey the ongoing nature of their acquaintance up to the present.