One day, Mary asked her mother, "Mum, what do people mean by saying they have a skeleton in the closet ?" Her mother paused thoughtfully and said, "Well, it's something that you would rather not have anyone else know about. For example, if in the past, someone in Dad's family had been arrested for stealing a horse, it would be a skeleton in his family's closet. He really wouldn't want any neighbor to know about it." "Why pick my family?" Mary's father said with anger. "Your family history isn't so good, you know. Wasn't your great-great-grandfather a prisoner who was transported to Australia for his crimes?"  "Yes, but people these days say that you are not a real Australian unless your ancestors arrived as prisoners." "Gosh, sorry I asked. I think I understand now." Mary cut in before things grew worse. After dinner, the house was quiet. Mary's parents were quite angry with each other. Her mother was ironing clothes and every now and then she glared at her husband, who hid behind his newspaper pretending to read. When she finished, she gathered the freshly pressed clothes in her arms and walked to Mary's closet. Just as she opened the door and reached in to hang a skirt, a bony arm stuck out from the dark depths and a bundle of white bones fell to the floor. Mary's mother sank into a faint , waking only when Mary put a cold, wet cloth on her forehead. She looked up to see the worried faces of her husband and daughter. "What happened? Where am I?" she asked. "You just destroyed the school's skeleton, Mum," explained Mary. "I brought it home to help me with my health project. I meant to tell you, but it seemed that as soon as I mentioned skeletons and closets, it caused a problem between you and Dad." Mary looked in amazement as her parents began to laugh madly. "They're crazy," she thought. Ks5u Mary's parents laughed madly at the end of the story probably because  _  .
They were mentally ill. They were over happy. They understood what had really happened. They both thought they had won the quarrel.
Question: One day, Mary asked her mother, "Mum, what do people mean by saying they have a skeleton in the closet ?" Her mother paused thoughtfully and said, "Well, it's something that you would rather not have anyone else know about. For example, if in the past, someone in Dad's family had been arrested for stealing a horse, it would be a skeleton in his family's closet. He really wouldn't want any neighbor to know about it." "Why pick my family?" Mary's father said with anger. "Your family history isn't so good, you know. Wasn't your great-great-grandfather a prisoner who was transported to Australia for his crimes?"  "Yes, but people these days say that you are not a real Australian unless your ancestors arrived as prisoners." "Gosh, sorry I asked. I think I understand now." Mary cut in before things grew worse. After dinner, the house was quiet. Mary's parents were quite angry with each other. Her mother was ironing clothes and every now and then she glared at her husband, who hid behind his newspaper pretending to read. When she finished, she gathered the freshly pressed clothes in her arms and walked to Mary's closet. Just as she opened the door and reached in to hang a skirt, a bony arm stuck out from the dark depths and a bundle of white bones fell to the floor. Mary's mother sank into a faint , waking only when Mary put a cold, wet cloth on her forehead. She looked up to see the worried faces of her husband and daughter. "What happened? Where am I?" she asked. "You just destroyed the school's skeleton, Mum," explained Mary. "I brought it home to help me with my health project. I meant to tell you, but it seemed that as soon as I mentioned skeletons and closets, it caused a problem between you and Dad." Mary looked in amazement as her parents began to laugh madly. "They're crazy," she thought. Ks5u Mary's parents laughed madly at the end of the story probably because  _  .
A. They were mentally ill.
B. They were over happy.
C. They understood what had really happened.
D. They both thought they had won the quarrel.
Answer: