The baby has been crying for fifteen minutes.

Explanation:

The given sentence is in the present perfect continuous tense. This tense is used to describe an action that started in the past, is still happening in the present, and may continue into the future. In this case, the action is the baby crying.

Present Perfect Continuous Tense:
The present perfect continuous tense is formed by using the present perfect of the verb "to have" (has/have), the past participle of the main verb (been), and the present participle of the main verb (crying).

Reasoning:
The sentence states that the baby has been crying for fifteen minutes. This indicates that the crying started in the past (fifteen minutes ago) and is still happening in the present. The use of "has been crying" suggests that the crying is a continuous action that has been going on for a duration of time.

The present perfect continuous tense is appropriate in this context because it emphasizes the duration of the action. It conveys the idea that the baby has been crying for a continuous period of time and is still crying at the present moment.

Example:
To further illustrate the use of the present perfect continuous tense, consider the following example: "I have been studying for three hours." This sentence implies that the studying started in the past and is still ongoing. It emphasizes the duration of the action, indicating that the person has been studying for a continuous period of three hours.

Therefore, in the given sentence, "The baby has been crying for fifteen minutes," the use of the present perfect continuous tense accurately conveys the ongoing, continuous nature of the baby's crying for the specified duration of time.