The correct answer is - (b) changing ocean circulation.
The ocean currents are very important when it comes to the climate. The movement of the tectonic plates though, over time, is changing their patters. The changes appear because of the movement of the land masses, so there can be situations where the ocean currents are interrupted by a moving land mass, or more space to be opened up for an already existing ocean current with the moving away of a land mass of its path. Those movements and spaces in the water bodies are affecting the direction and the temperature of the ocean currents, and those changes will reflect on the climate on the regions that they are influencing.