Question

it difficult to do sth 和it is difficult to do sth 的区别

Answer 1

it difficult to do sth: difficult修饰to do sth。例如：
I feel it difficult to speak English.
其中it指代speak English,difficult修饰speak English。

It is difficult to do sth:常见句型，意思是:做什么事...难。

Answer 2

it difficult to do sth不完整吧，这个结构只有主语成分，不能成句子，其中difficult to do sth是省略的定语从句，修饰it的

Answer 3

你就把"do
sth"换成动词短语原型
一般情况下to后面接动词原形
it
is
difficult
to
get
up
early
it
is
really
difficult
to
eat
while
running