As the years passed, many occasions—birthdays, awards, graduations — with Dad’s flowers.

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A. are marked
B. were marked
C. have marked
D. had marked
解析：由于句中增加了插入成分birthdays, awards, graduations，使得句子的主语与谓语were marked分离，从而增加了考生对句子理解的难度。根据句意，空格处应填被动语态; 再根据句中的passed的时态特点可知，空格处也应用一般过去时，故选B。