humility is considered a vitue .a vitue前不用as,

英语句子如果省略一两个次要的单词不改变意思（或导致歧义）,
那些单词是可以省略的.
就拿你的例句：
humility is considered a virtue
完整的句子其实是
Humility is considered to be a virtue
或
Humility is considered as a virtue
这里 to be 和 as 常被省略,因为听者不会误解句子的含义.
而下面的句子
An ensemble of things is a group of things considered as a whole
把 as 省去：
An ensemble of things is a group of things considered a whole
后就不通顺、不清楚了
但有些人会这样说：
An ensemble of things is a group of things considered as whole
2、do you have one more yuan,Sir/Madam?
More 是副词,修饰 one
a ticket home
完整化其实是
A ticket to go home
或
a ticket for home
第一句home是副词,修饰 go
第二句home 是名词
为什么是 we're short one yuan 而不是 we short one yuan?
We’re = we are,
Are 是动词,没有动词句子不完整.
short 是形容词,
是成语性的用法,
We are short = 我们缺少
其他含有short 的成语有
fall short,不合格,不及格,不够
cut short,即刻结束,裁短,削减
for short,简单地说
in short,一言以蔽之,总的来说
英语是很灵活的语言,学语言最好不要从语法的角度过度研究、分析
而从多读、多听去学.
这和学汉语没两样.
希望帮到了你.