Answer:
C. When I looked into the small rectangle, I saw a face looking back at me but I didn’t recognize it.
Step-by-step explanation:
The original sentence is written in present indefinite tense, so when it is changed to past tense, it should be past indefinite. Moreover, to make the sentence structure parallel, all of it clauses being changed to past tense. Out of the given options, only C has correctly written sentence in past tense (all clauses changed to past tense). Options A, B, and D have at least one clause not changed to past tense. SO they are all incorrect.