Thank you for the opportunity to help you with your question!
Ok, let's remember the relationship between Celsius degree and Kelvin: ºC = K - 273.15 . So an interval of one Celsius degree is equivalent to an interval of one Kelvin (option a) since there's a linear relationship with a slope of 1, the equation can be written like: ºC = 1*K - 273.15 (its slope 1).
Please let me know if you have any doubt or question.
Please let me know if you need any clarification. I'm always happy to answer your questions.