Explanation:

When using the past perfect tense in English, we typically use the form "had + past participle" to indicate that an action was completed before another past action or event. In this sentence, the action of typing was completed before the speaker arrived at the office. Hence, the correct answer is "had already finished".

Breakdown of the sentence:
- Subject: Adams
- Verb: typing
- Adverb: already
- Time: when I arrived at the office

Past perfect tense:
The past perfect tense is used to describe an action that happened before another past action or event. In this case, the action of finishing typing (past perfect tense) happened before the speaker arrived at the office (simple past tense).

Importance of "already":
The adverb "already" is used to emphasize that the action of typing was completed before a specific time (when the speaker arrived at the office). It indicates that Adams finished typing at some point in the past, and by the time the speaker arrived at the office, the action was already completed.

Putting it all together:
By using the past perfect tense "had already finished", the sentence conveys that Adams had completed the action of typing before the speaker arrived at the office. It emphasizes that the action was finished before a specific point in the past, which is when the speaker arrived.

Therefore, the correct answer is "Adams had already finished typing when I arrived at the office."