Which one is correct?

[Quinceps]

a) "What effects can an oil spill have?"

b) "What effects can have an oil spill?"

As in a), I was taught that questions are usually made by inverting the subject and the first verb (operator "can") of an affirmative sentence.

However, I found b) on a handout on how to write a report in English, with the subject after the complete verb phrase ("can have") on Google (I know it's not a very good reference, though).

Which one is better? Are both correct? If you don't mind also telling me why, I'd be very grateful.

[Alan]

Only (a) is correct.