There is ----------milk.Let's buy some.

D
few/a few修饰可数名词 little/a little修饰不可数名词
few,little表否定含义
a few,a little表肯定含义
都是很少的意思
这里milk不可数,而且后文Let's buy some.表示少得几乎没有了（所以才要买）,所以用little