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

Susan finally arrived at the party at midnight, but by then, most of the guests ________.

had left

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

☀ had left

The sentence would read: "Susan finally arrived at the party at midnight, but by then, most of the guests had left."

Explanation: In this sentence, you're describing an action that happened before Susan's arrival at the party. The past perfect tense, "had left," is used to indicate that the guests left before a specific past point in time (midnight, in this case). The other options don't form a correct sentence:

• Having left: This is a participle phrase and doesn't work as the main verb in the sentence.

• Have left: This is the present perfect tense, which doesn't convey the correct past time relationship with Susan's arrival at midnight.

• Left: This is the simple past tense, which doesn't indicate that the action (guests leaving) occurred before another past action (Susan's arrival).