transporting oil over the ocean surface drilling for oil on the ocean floor polluting land with oil that reaches the oceans in runoff polluting air with oil that reaches the ocean in precipitation
I gave my students this multiple choice question: Just under half the oil that enters ocean water comes from natural oil seeps on the ocean floor. Just over half the oil in the oceans comes from human activities. Which human activity contributes the most oil to the oceans?

Only one answer is correct among these 4 choices:
- transporting oil over the ocean surface
- drilling for oil on the ocean floor
- polluting land with oil that reaches the oceans in runoff
- polluting air with oil that reaches the ocean in precipitation

Could you tell me which one is correct?

transporting oil over the ocean surface