The report concluded that, the new policy would have significant financial implications.
Correct: B
Option B is correct because a comma should not be used to separate 'that' from the clause it introduces when 'that' functions as a subordinating conjunction. The phrase 'that the new policy would have significant financial implications' is a noun clause acting as the direct object of 'concluded,' and it should not be separated by a comma. Options A, C, and D incorrectly insert commas or semicolons.