Final answer:
Samuel Pepys likely saw marks on doors during the Great Plague of London, which indicated that the occupants were infected and the house was quarantined, causing him unease.
Step-by-step explanation:
The question refers to the experiences of Samuel Pepys, a naval administrator and Member of Parliament who is most known for the diary he kept during the mid-17th century. This diary provides a first-hand account of many major events in London's history, including the Great Plague of London in 1665. When the student asks "What did Pepys see upon house doors that made him uneasy?", they are likely referring to the marks that were placed on the doors of homes affected by the plague. These marks were used to indicate that the occupants were infected, and such houses were often quarantined to prevent the spread of the disease. The sight of these marks would naturally cause unease, as they were a grim reminder of the pestilence ravaging the city.