问题：

[单选,材料题] __________

根据以下内容，回答下面的题目。
The death of a child, _51_ one’s own child,is something the mind can hardly comprehend．It seems togo _52_ nature．The end of a life that is still forming_53_ has just begun is an almost unthinkable cruelty．
But it happens．Parents sometimes must witness the illness and death of the children_54_ whom they gave birth．And _55_ will ever fill theempty place that the dead child leaves behind．Parents_56_ to die before their children, which is the natural order of life events．When the situation is reversed and a child dies _57_ the parents itseems wrong．
Yet we never know why one person dies andanother lives．But we do know _58_ a child is gone, theparents still have a future, as grey and worthless as it may at first seem．Death may take the child, but the love never _59_．
The sorrow after a child’s death is one ofthe longest and hardest type of _60_ to live with．And ittakes long to deal with the parents’ own emotions．
__________

A . and
B . or
C . but
D . so