Help me please Explain possible circumstances under which an adult child may
have undue influence in a relationship with an elderly parent.

i think seeing their grand parent arguing with a parent, probably would make them question a lot, and they might evem stay away from them for a while, though, i may have took your question wrong, very sorry

Explanation:

if your meaning a situation where the child either wants to get away from them or they feel apart from them, this might help.

answer; i believe the correct answer is (sales promotion;

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