Anarrow channel or slab of a mineral that is different from the surrounding rock is called a
a. vein.
b. solution.
c. crystal.
d. metal.

The correct answer is A) Vein.

Vein is a narrow channel or slab of a mineral that is very different from its surrounding rock. It is a sheetlike structure of minerals ( within a rock), which is formed when minerals are carried by aqueous solution and get deposited through precipitation.

On the contrary, solution is prepared by dissolving one substance in another, crystal is a repeating pattern of particles of minerals ( like diamond crystal made up of carbon) and metal is a hard material, which possesses properties like ductility, malleability, thermal and electrical conductivity etc.

Thus, A) is the right  answer.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.