（六）放射性同位素，是指化学元素中具有相同原子序数，但质量不同且能发生放射性衰变的核素。
"There's the urine, the droppings," he says. "One time there was a carpet leading up to the altar that became absolutely sodden with urine and droppings and had to be thrown away. They also destroyed the brass work."
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