It's being estimated that dinosaurs lived on Earth from about 237 million years ago to about 66 million years ago. So answers B and D are definately too "old", while answer A is too "young". I'd pick answer C as it's most probable.
It can be one of two things.
First, it can be due to global warming.
Second, it can be due to the rotation of the sun. When the sun rotates, it can change it latitude causing it to hit at different points onto different areas of the world.
