Final answer:
The correct answer is option 4) so.
Step-by-step explanation:
The correct answer to fill in the blanks would be option 4) so.
In the given sentence, 'We were ________. ________...late that we missed the business meeting that took place an hour ago,' the word 'late' indicates that the first blank should be filled with an adverb that intensifies the degree of lateness. The second blank requires a conjunction or word that indicates a result or consequence of the lateness. Among the given options, 'so' is the most appropriate choice as it functions both as an adverb to intensify 'late' and as a conjunction to show the consequence of being late.