Answer:
B. Is curved
Step-by-step explanation:
Earth surface is curved, not flat. Due to the curved earth surface, some part of the earth surface gets direct and straight solar radiations than others.
For example, the regions located near equator get direct and straight solar radiations imparting them higher temperature. On the other hand, the regions near poles obtain slant solar radiations. This is the reason that polar regions have colder climatic conditions.