Answer:
E-mail
Step-by-step explanation:
Text messages, instant messages, and social networking are all generally considered as informal methods of communication which are used to communicate informal information, such as a the change in a meeting time if schedules have been adjusted during a factory tour.
Secondly such informal means of communication might not be ideal for use to a colleague in another office as the relationship would not be very personal but official.
Since Caroline needs information from a coworker in another office about an upcoming salespromotion, she is better off sending her request via e-mail