word choice - What is correct in English - "I am sorry it took so long" vs "I am sorry that it took so long"

• "I am sorry it took so long"



• "I am sorry that it took so long"

Are both of these sentences correct? If so, what is the difference between them?

Answer

That in this case is optional, so both are grammatically correct.
Depending on the communicative situation you may slightly decide for one over the other.
In normal speech situations I'd probably use the first one but contracted I'm sorry it took so long.