He was stunned by her plea. What must I do? He asked himself in sheer agony. What man on earth could deny a child the chance to live?
这句的on earth是到底还是在世上的意思？和on the earth的不同之处
英语中有的词汇，用在特殊疑问词或特殊疑问词修饰的名词之后，加大句子语气，意为“到底；到底”，这类词汇是：
in Gods name,
in Heavens name,
on earth,（不是on the earth）
in the world,
the hell,
in hell
What on earth are you doing now?
你到底在做什么?
What in God s name was that huge bang ?
到底是什么砰的一声响？
What in Heavens name are you doing?
你到底是在做什么！
Who in the world is that man taking to your wife?
和你老婆说话的那个人到底是哪个？
You searched the rooms one by one like this. When on earth can you find it?
你如此一个房间一个房间地找，什么时间能找到啊？
Where the hell were we going?
大家这是要到哪儿去？
