Final answer:
The correct sentence is option A: When Washington held the first presidential barbecue in 1793, he roasted a five-hundred-pound ox for the party.
Step-by-step explanation:
The correct sentence is option A: When Washington held the first presidential barbecue in 1793, he roasted a five-hundred-pound ox for the party.
Option A corrects the sentence by adding the conjunction 'when' at the beginning to indicate the time relationship between the two events. This makes it clear that Washington roasted the ox during the first presidential barbecue in 1793.