What is extrusive rock​

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Explanation:

Extrusive rock, any rock derived from magma (molten silicate material) that was poured out or ejected at Earth’s surface. By contrast, intrusive rocks are formed from magma that was forced into older rocks at depth within Earth’s crust; the molten material then slowly solidifies below Earth’s surface, where it may later be exposed through erosion. Extrusive rocks are usually distinguished from intrusive rocks on the basis of their texture and mineral composition.

Extrusive rock, any rock derived from magma (molten silicate material) that was poured out or ejected at Earth's surface

Explanation:

i'm sure the answer you are looking for would be

a. an ice age

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