The Logic: The "Desensitization" Effect
The sentence describes a psychological phenomenon:
- The Cause: People view images of "maltreated pets" many times ("more than a few times").
- The Result: They stop donating.
- The Reason: Repeated exposure to distressing images often leads to a "numbing" effect where the viewer no longer feels the emotional impact.
- The Goal: We need two synonyms that mean accustomed to something unpleasant or emotionally toughened.

The Correct Answers:
A. inured
D. hardened
- Why they work: *Inured means to accustom someone to something, especially something unpleasant. If you are inured to the sight of suffering, it no longer moves you to action.
- Hardened means to become tough or insensitive. A "hardened" viewer is no longer susceptible to the emotional "pull" of the advertisement.
- Both words describe the specific psychological state of being "numb" to repeated stimuli.

Why the others fail:
- B. miserly: This means stingy with money. While they are donating less, the sentence is explaining why their feelings changed, not labeling their character as inherently greedy.
- C. disgusted: If people were disgusted, they might actually be more likely to want to help, or they might turn away, but "disgusted" doesn't capture the "repeated exposure" logic as well as "inured."
- E. bored: While they might be tired of the ads, "bored" is too trivial a word for the context of animal maltreatment.
- F. overwrought: This means deeply agitated or over-excited. If people were overwrought, they would be having an extreme emotional reaction, which would typically drive donations up, not down.

Final Completed Sentence

Animal welfare charities have found that extensive advertising, especially over the Christmas period, can actually drive down the volume of donations as people who view images of maltreated pets more than a few times rapidly become inured / hardened.