Answer:
The correct answer is option A, that is, ice caps.
Step-by-step explanation:
The part of the planet Earth covered by water or ice is known as the hydrosphere. It comprises lakes, oceans, rivers, polar ice caps, and glaciers. The polar ice caps and glaciers are the only elements of solid found in the hydrosphere.
The other options, that is, lakes and rivers are also a part of hydrosphere but they are in liquid form. While rainforest and rocks and minerals are the parts of the lithosphere, not hydrosphere.