Which sentence does not contain any punctuation errors?

AThinking about it now, I realize that I was wrong.
BThinking about it now I realize, that I was wrong.
CThinking about it now I realize that I was wrong.
DThinking, about it now, I realize that I was wrong.

Verified Answer :

The sentence that does not contain any punctuation errors is A) Thinking about it now, I realize that I was wrong.
There has to be a comma after now, because the whole order in the sentence is inverted.

The answer to the English question presented above would be letter a. Thinking about it now, I realize that I was wrong. The sentence that does not contain any punctuation errors would be 'Thinking about it now, I realize that I was wrong.'. All the other choices are not applicable.