Read the passage on crude mineral oil and answer the question: According to the passage, why do layers of sedimentary rocks lead to the formation of oil deposits?

Introduction / Context:
This reading comprehension question examines your understanding of the mechanism by which sedimentary rocks contribute to the formation of crude oil. The passage explains how pressure and heat over long periods transform organic deposits into oil. The exam tests whether you can connect these ideas accurately instead of relying on guesswork.

Given Data / Assumptions:

• The passage explains that layers of sedimentary rocks become thicker and heavier.
• It states that their pressure produces heat, which transforms the tiny carcasses into crude oil.
• Options present different reasons related to heaviness, oxygen, hardness, and pressure.
• We assume the candidate has read and understood the part of the passage describing this transformation.

Concept / Approach:
The central concept is that thick layers of rock exert pressure on the organic materials trapped below them. This pressure generates heat, and over millions of years, the combination of pressure and heat chemically alters the organic remains into crude oil. The correct option must include both the pressure and the transformation of animal and plant deposits into oil, not just a vague reference to hardness or squeezing.

Step-by-Step Solution:
Step 1: Recall the key sentence from the passage: "The layers of sedimentary rocks become thicker, and heavier. Their pressure produces heat, which transforms the tiny carcasses into crude oil." Step 2: Identify the two important processes: pressure producing heat, and heat transforming organic matter into oil. Step 3: Examine option A: "their pressure produces heat and turns deposits of animal carcasses and plants into oil." This repeats the idea from the passage with minor rephrasing. Step 4: Examine option B: "it turns heavy and shuts out the oxygen." While shutting out oxygen is mentioned earlier in the passage as preventing decomposition, it is not the reason why sedimentary rocks lead to oil deposits. Step 5: Examine option C: "it becomes hard and forms into rocks to squeeze oil." The passage does not say that rocks simply squeeze out oil; it explains transformation by heat. Step 6: Examine option D: "it becomes light and soft and applies pressure to produce oil." This contradicts the text (rocks become thicker and heavier, not light and soft).

Verification / Alternative check:
Re-reading the relevant part of the passage confirms that the final stage of oil formation involves increased pressure from accumulating rock layers, which generates heat. This heat drives chemical changes in the organic material, creating crude oil. In contrast, the shutting out of oxygen is earlier described as preventing complete decomposition, not directly as the cause of oil formation. Therefore, the only fully accurate and complete option is A, which clearly connects pressure, heat, and transformation of organic deposits.

Why Other Options Are Wrong:

• it turns heavy and shuts out the oxygen: This partially reflects an earlier stage where sedimentary rock shuts out oxygen, but it does not describe how oil is produced from organic deposits.
• it becomes hard and forms into rocks to squeeze oil: The passage does not say that oil is already present and being squeezed out; instead, it emphasises chemical transformation under heat.
• it becomes light and soft and applies pressure to produce oil: This is directly opposite to the description in the passage, where the layers become thicker and heavier, not light and soft.

Common Pitfalls:
Students sometimes confuse different stages of the process described in the passage, mixing up the role of oxygen exclusion with the role of pressure and heat. Others may rely on everyday ideas like squeezing oil out of rocks, which are not scientifically accurate. To perform well in such questions, focus on the exact sequence in the passage and distinguish each step: first, deposits are covered, oxygen is excluded, and then pressure and heat gradually transform the organic material into oil.

Final Answer:
Sedimentary rocks lead to oil deposits because their pressure produces heat and turns deposits of animal carcasses and plants into oil.