Answer Explanation

[PASSAGE] "When magma cools slowly deep inside the crust, it forms intrusive igneous rocks, like granite, which have large, visible crystals. In contrast, when lava cools rapidly on the surface, it forms extrusive igneous rocks, like basalt, which typically have very small crystals or a glassy texture." This states that the speed of cooling directly impacts the size of crystals in igneous rocks. [WHY CORRECT] Option 2, "The speed at which the molten rock cools," is correct because the passage explicitly links slow cooling to large crystals and rapid cooling to small crystals, making cooling speed the determining factor for crystal size. [TRAPS] Option 1 ("The chemical composition of the molten rock") is wrong because the passage does not mention chemical composition as influencing crystal size. Option 4 ("The amount of pressure applied during formation") is wrong because while pressure is mentioned in relation to metamorphic rocks, it is not cited as a factor for igneous rock crystal size. [TIP] When answering detail questions, look for direct statements or explicit relationships between concepts in the passage. Avoid making assumptions or bringing in outside knowledge.

Why the Other Options Are Incorrect

• Option A (“The chemical composition of the molten rock.”) swaps the cause and effect described in the passage.
• Option C (“The age of the rock when it is discovered.”) attaches the right fact to the wrong subject.
• Option D (“The amount of pressure applied during formation.”) states information not mentioned in the passage.

Key Language in Context

The language describing Geology rewards close reading: notice contrast markers, hedging, and emphasis, since TOEFL detail items hinge on nuance rather than matching keywords.

Skill Takeaway

Locate the exact supporting line in the text instead of relying on memory.