Which of the following cycles does not involve living organisms?
a. carbon cycle
b. oxygen cycle
c. rock cycle
d. nitrogen cycle

The right answer is c. rock cycle.

It is clear that the rock cycle does not include living beings. So the cyces of the rocks concerns only the geosphere and not the whole biosphere.

We divide the rocks into 3 major types: igneous, sedimentary and metamorphic. The rocks all come, despite their great diversity of color and texture, from 3 major modes of formation. Igneous rocks, also called magmatic, are derived from molten materials from within the Earth (magma). Sedimentary rocks result from the compression of debris that has accumulated in some places for long periods of time. Finally, metamorphic rocks come from the transformation of other rock types that have been subjected to high temperatures and pressures by high geological activity.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)