Final answer:
In the sentence 'I was at the conference but I did not run into them,' the word 'but' should be followed by a comma. The correct answer is B, 'did'
Step-by-step explanation:
In the sentence 'I was at the conference but I did not run into them,' the word 'but' should be followed by a comma. The word 'but' is a coordinating conjunction that connects two independent clauses. When coordinating conjunctions join independent clauses, a comma should be used before the coordinating conjunction to separate the clauses. Therefore, the correct answer is B, 'did'.
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