Final answer:
Francesca's tone in the given sentences is commanding.
Step-by-step explanation:
The word that best describes Francesca's tone in the given sentences is d. commanding. Francesca tells Ira and Michael what they need to do without any room for negotiation or further warning, indicating a take-charge and authoritative demeanor.
Additionally, she specifies the exact amount of time they are to be out of the water (fifteen minutes) and informs them that she will be the one to decide when they can return. This level of control and direction clearly indicates that Francesca is in charge and expects her instructions to be followed without question.