The given statement is:
If we are having sushi for dinner, then it is not Sunday.
The statements are:
p: We are having sushi
q: It is not sunday
The statement is given by:

Negation of p or q.
The statement "We are having sushi for dinner and its sunday" is:

Option A is negation of the given statement.
The stetement "If we are not having sushi for dinner, then it is Sunday." is:

Option B is neither.
The statement "It is not Sunday and we are not having sushi for dinner" is given by:

Option C is neither.
The statement If its Sunday, we are not having sushi for dinner is given by:

So option D is equivalent to the statement.