Answer:
C
Explanation:
The restructioning of this sentence is dependent on the action of the cargo. The cargo does not have mind of its own. The commas describe the action of the cargo. The correct phrase to you is:
In January 1994 an oil barge ran aground off the coast of San Juan, Puerto Rico, and its cargo of 750000 gallons leaked into the ocean, while causing the pollution of the city's beaches.