Working diligently through the night the team managed to meet their deadline a remarkable feat considering the obstacles they faced.
Correct: A
The sentence begins with an introductory participial phrase ('Working diligently through the night'), which must be followed by a comma. The phrase 'a remarkable feat considering the obstacles they faced' acts as an appositive, providing an explanation or elaboration of 'their deadline'. A dash is an effective way to introduce such an emphatic appositive, particularly when it comes at the end of a sentence and explains the preceding clause. Option A correctly places a comma after the introductory phrase and uses a dash to introduce the explanatory appositive.