Final answer:
The part of the sentence that tells something the reader likely knows is that people usually use a pen or pencil to write in a journal.
Step-by-step explanation:
In the sentence, 'Samuel wrote with a pen or pencil in his journal every morning before school,' the part that tells something the reader is likely to know already is "People usually use a pen or pencil to write in a journal." This can be seen as common knowledge because pen and pencil are standard tools for writing in journals or on paper in general. Options A, B, and D could be considered less likely to be known or assumed by all readers, as they relate to personal habits that can vary widely from one individual to another.