I understand (that) you have

[tiantian888]

I understand that you have many difficulties.
I undersand you have many difficulties.
I understand, you have many difficulties.

Could you please tell me which one is more standard English and more concise? Thank you very much for your great help.

 

[Lamialol]

i would say I understand that you have many difficulties

 

[pismo]

The first and second are equivalent, since it is common to drop the conjunction "that."

There is a subtle difference between those two and the third.

"I understand that you have many difficulties" = "I am aware that..."

But the phrasing of the last implies that you may be about to make a point.

"I understand, you have many difficulties. However, so does everyone else."

Or "I understand, you have many difficulties, but you still may not do that."

The first or second are your best choices.