The correct answer is A) 1.5%. In accordance with the MARPOL Annex VI regulations, the maximum allowable sulfur content for fuel burned in an emissions control area (ECA) is 1.5% in the absence of an exhaust gas cleaning system. This is a requirement set forth by the International Maritime Organization (IMO) to limit sulfur oxide emissions and improve air quality in designated ECAs. The other answer choices are incorrect because they exceed the 1.5% sulfur limit for ECAs. For example, 3.0%, 4.5%, and 6.0% would all violate the ECA regulations and are not permitted without the use of an approved exhaust gas cleaning system.