Earth: The Ground Beneath Our Feet
The question you've asked is a form of a riddle. Each line is pointing to a specific letter. For example, 'my first is in water but isn't in air' would be the letter 'w' since 'w' is present in 'water' and not in 'air'. Similarly, 'my second's in ocean and sea, but not there' points to the letter 'a', and so forth. If you continue this pattern, the answer becomes 'Earth'. Therefore, the answer is b) Earth.
The riddle is describing different elements of the Earth, such as water, ocean, sea, river, and stream. The final clue, 'my whole can be found under everyone's feet', suggests that the answer is something that is universally present on the Earth's surface and can be stepped on, which is the Earth itself.
Soil, ground, and sand are also related to the Earth, but in this specific riddle, the ultimate answer is Earth. The Earth is our planet, and it is the ground beneath our feet, providing the foundation for life to thrive. Understanding the riddle helps us appreciate the significance of the Earth and the natural elements that make up our environment.