Two types of genes play major roles in regulating the cell cycle: proto-oncogenes encourage cell division, while tumor-suppressor genes inhibit cell division. the balance between these two types of genes may be disrupted by naturally occurring or environmentally caused a) proteins. b) mutations. c) inhibitors. d) cell cycle clocks.

B. Mutations

Explanation:

Mutations are the random changes in the genome of the organisms. Mutations in proto-oncogene or tumor suppressor gene can result in loss of balance between these two types of genes. It causes loss of control over cell cycle. Mutations can be caused by natural or environmental factors such as X-rays, ultraviolet radiations as well as certain toxins.

d. groundwater flows through the subsoil and deposits minerals.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.