What must happen for most areas on earth to experience all four seasons? a. the sun must reach its highest point in the sky. b. the northern hemisphere must experience winter. c. the axis must be tilted at a certain angle that remains unchanged. d. the north end of earth's axis must always point away from the sun.

The axis must be tilted at a certain angle that remains unchanged.

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The correct answer is option C, The axis must be tilted at a certain angle that remains unchanged.

Explanation:

The seasons of the earth are caused by the tilt of earth’s axis. During different time period of a year, the extent of sun rays reaching directly to the earth varies. During the winter season, the southern hemisphere of the sun is tilted away from the sun while the northern hemisphere facing the sun experiences summer season. This cycle rotates and thus the season changes.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.