Water is very good at absorbing heat, making it incredibly unlikely that the heat from a volcanic explosion will spread thousands of miles.
The addition of lava into the ocean would not be significant enough to raise sea levels on the other side of the ocean without there being significantly larger problems (like the planet being cracked).
Volcanic eruptions do result in tectonic plate movement, but it is unlikely that an eruption thousands of miles away will trigger any noticeable change.
This leaves B, which describes the phenomenon believed to have killed the dinosaurs and to have caused major climate abnormalities in 1816. When large amounts of ash go into the atmosphere, they are spread by air currents in the same way a hurricane can travel from Africa to North America. The ash cloud would obscure the Sun, reducing the amount of solar radiation reaching the surface and thus decreasing temperatures.
