Final answer:
Without more context, it's not possible to determine the specific time period when Martin felt nostalgic, grateful, and affectionate towards his grandpa. The emotional state provided does not give the necessary historical context.
The correct choice is 20th century.
Step-by-step explanation:
The time period in which Martin may have felt nostalgic, grateful, and affectionate towards his grandpa could not be accurately determined without additional information.
Each of the provided options-a) Victorian era, b) Renaissance period, c) Industrial Revolution, d) 20th century-represents a distinct period in history that could be associated with different contexts for Martin's feelings. However, the question suggests an emotional state rather than providing a historical context, making it impossible to select the correct time period with the information given.
Martin likely felt nostalgic, grateful, and affectionate towards his grandpa during the 20th century. Nostalgia refers to a sentimental longing or wistful affection for the past, and Martin's feelings towards his grandpa would fit this definition.
Gratitude and affection are emotions that can be felt towards loved ones, and it's reasonable to assume that Martin would have these feelings towards his grandpa during this time period.
The correct choice is 20th century.