The document discusses the present perfect continuous and past perfect tenses.
[1] The present perfect continuous tense uses "have/has been + verb+ing" to describe an action that began in the past and has recent completion or is still ongoing. It can express duration.
[2] The past perfect tense uses "had + past participle" to describe an action that was completed before another past action. The first action expressed must be in the past perfect tense.
[3] The simple past tense can be used with two actions to indicate one occurred shortly after the other without specifying which came first.