Rearrange the following parts of the sentence to form a coherent paragraph about the achievements of science and their real basis. P: But the achievements of science have not come to human beings as a ripe apple falls in the lap of a man sitting under an apple tree. Q: Science is not just the result of simple observation and casual experience. R: It is, on the other hand, the result of centuries of hard work done by human beings, often at the risk of their own life or health. S: There is no doubt that science has been the greatest boon to human beings so far.

Introduction / Context:
This rearrangement question focuses on the theme of science as a boon and the effort behind scientific achievements. The sentences discuss the benefits of science, clarify that these benefits did not arrive effortlessly and explain how they are based on hard work rather than mere observation. To answer correctly, we must identify how an author would typically introduce such an idea, contrast appearance and reality, and conclude with an explanation of the true basis of scientific progress.

Given Data / Assumptions:

• S states that there is no doubt that science has been the greatest boon to human beings.
• P adds that the achievements of science did not come easily like a ripe apple falling into a person's lap.
• Q says science is not just the result of observation and experience.
• R explains that it is the result of centuries of hard work at serious personal risk.
• We assume the paragraph will start with a general statement about science, then explain that its achievements are not effortless, and finally show the true reason behind those achievements.

Concept / Approach:
The main approach is to:

• Locate the general introductory statement that sets the tone; here, S clearly states a broad claim about science as a boon.
• Identify the contrast or qualification to that statement using words like "But" in P.
• Connect Q and R, which form a logical pair: Q negates a simplistic view, and R supplies the correct view.
• Ensure that pronouns like "It" in R refer back clearly to "Science" in Q or S.

This method helps us see the natural progression from praise to misconception removal to explanation.

Step-by-Step Solution:
Step 1: S is a natural opening sentence because it broadly states that science is the greatest boon to human beings and needs no prior context. Step 2: P follows S well because it begins with "But", which contrasts the boon of science with the reality that its achievements have not fallen effortlessly into our laps. Step 3: After clarifying that achievements are not effortless, Q further refines our understanding by saying that science is not just the result of observation and experience. Step 4: R comes immediately after Q and uses "It is, on the other hand" to provide the real explanation: science results from centuries of hard work, often risky and demanding. Step 5: Reading S-P-Q-R as a full paragraph gives a smooth argumentative flow from praise, to warning against a simplistic view, to correction and final explanation.

Verification / Alternative check:
Reading SPQR as a continuous paragraph confirms the logic. The first sentence praises science; the second adds that these achievements did not come easily; the third clears misconceptions about the process behind science; the fourth provides the hard work explanation. Any other order disrupts the structure. For example, QPRS begins with a somewhat technical statement about what science is not, which is less natural as an opening. SQRP or QRPS place "But" P or "on the other hand" R in positions where the contrast is unclear or the referent of "It" is not clearly established.

Why Other Options Are Wrong:

• QRPS: Starts with Q, which feels abrupt because it gives a negative without first stating the positive value of science.
• QPRS: Delays the broad boon statement S till the end, which weakens the introduction and conclusion.
• SQRP: P is not placed immediately after S, so the contrast introduced by "But" in P gets lost.

Common Pitfalls:
One common error is ignoring logical connectors like "But" and "on the other hand", which are vital for determining correct order. Another mistake is assuming that any sentence that looks general, such as Q, can start a paragraph even when it actually functions as a correction of a previous misconception. Examine attitude markers like "no doubt", "but", "not just" and "on the other hand" carefully, because they reveal the author's argumentative strategy.

Final Answer:
The correct sequence is SPQR, so the correct option is SPQR.