You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

[EX Q]: What is the MAJOR reason Earth has seasons?  
 (A) Earth has a moon (B) Earth has a tilted axis (C) Earth has a magnetic field (D) Earth has an elliptical orbit
[EX A]: B

[EX Q]: Which best describes a characteristic of the jet stream?  
 (A) It forms a boundary between a cold air mass and a warm air mass. (B) It creates the high winds around the eye of a hurricane. (C) It forces the hot air along the equator to rise to areas in North America. (D) It causes high pressure air masses to rotate clockwise.
[EX A]: A

[EX Q]: A cow and a frog have similar bone structures in their forelimbs. Both have phalanges, radius, ulna, and humerus bones. However, the cow and frog are animals with very different life cycles from each other. Which most likely describes why the body structures of these animals are so similar?  
 (A) Both have undergone similar mutations. (B) Both descended from a common ancestor. (C) Both reacted similarly to environmental pressures. (D) Both spread out from the same geographical region.
[EX A]:
B