The correct answer is remote grandparents.
Remote grandparents refer to grandparents who only occasionally spend time with or interact with their grandchildren due to physical and/ or emotional separation. Grandparents might be physically and/ or emotionally separated from their grandchildren due to reasons such as living far away from each other or due to a divorce of the children's parents. Since Luisa and Mark only see and spend time with their grandchildren during holidays, they can be considered remote grandparents.
Leaches were placed on top of the victim to remove "bad blood" what people did not know back then was that leaches remove 'good' and 'bad' blood alike.
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D. collecting biological specimens. Darwin went to the Galapagos islands to study evolution