请视原句：
But few will be as sensible and considerate when making the longjourney of life on board abig 'social' or 'global' train.
请问该句中的词组 on board 后为什么可直接跟名词？
But few will be as sensible and considerate when making the long journey of life on board a big 'social' or 'global' train.
请问该句中的词组 on board 后为什么可直接跟名词？
【答】on board 可以作为副词、形容词或者介词用，在这里作介词。《英汉多功能词典》新编升级版等词典中有例句。
