advantage的主要意思是“优势，好处”，为可数名词，常用于短语take advantage of sth
an obvious advantage
显著的优势
He took advantage of her good nature
他利用了她脾气好这个特点。
They took full advantage of the hotel's facilities
他们充分利用旅馆的设备.
What is the advantage of using nuclear power?
使用核能有何好处?
merit的主要意思是“优点，长处，好处，可取之处”，是可数名词，也是不可数名词。
Having worth, merit, or value; useful or valuable
有价值的具有价值或优点的；有用的或有价值的
As a top manager, he should appoint none but people on their merit
作为一位总经理，他应该任人为贤。
People may not like her, but she has her merits.
人们也许不喜欢她,但她也有她的优点。
He will judge the case solely on its merits.
他将完全根据是非曲直审理这一案件。
virtue的主要意思是“美德，品德，优点”，主要从事物的品质或价值的角度讲优点。
virtue and vice
善与恶
a lady of easy virtue
放荡的女人
Virtue will prevail against evil.
美德定将战胜邪恶.
Fidelity to engagement is a virtue.
信守诺言是一种美德。
She planted the seeds of virtue in her children when they were young.
孩子们小的时侯, 她就在他们心田里播下了道德的种子。
