abit of+[C]or[u]?

a bit of 后面加不可数名词。
a little后面加不可数名词或者形容词。
a bit后面加形容词。
例句：There is a bit of water in the bottle.
there is a little water in the bottle.
it's windy.it's a little cold.
it's windy. it's a bit cold.
a bit of 后接不可数名词，相当于 a little
如： a bit of water = a little water
a bit of milk = a little milk
另外，还要注意这个常用词组：“have a bit of a cold(有点儿感冒)”，“cold（感冒）”虽然是个不可数名词，但习惯上要加a

a bit of+[u]
因为a bit of＝a little (＋un.)

u

a bit of 一般接不可数名词
但是在 它后面加上 a 就可以接可数名词
列子：
a bit of a problem “有点麻烦”。
当然你把a bit of a 看成一个固定搭配也可以。