a 加的是可数名词
some 加的是可数名词和不可数名词
a tin of beans 一瓶大豆
some oil 一些油
some tobaccos 一些烟草
cut some wood to make a fire
Put some more wood on the fire.再往火里添点儿柴le
i like the curtains in this room
a 是泛指
the 是特指
some 一些