Rearrange the following parts of the sentence to form a coherent paragraph about tsunami waves and their behaviour. P: In addition, tsunamis move throughout the depth of the ocean and not just on its surface. Q: A tsunami wave is not much different in height compared to other waves in the open ocean. R: That is why a tsunami generally goes unnoticed in the open ocean. S: But due to its very long wavelength, it piles up when it approaches land.

Introduction / Context:
This rearrangement question explains why tsunami waves are often unnoticed in the open ocean but become destructive near land. The four parts speak about tsunami height, tsunami motion through the ocean depth, how they go unnoticed and how they pile up when nearing land. The correct paragraph will start with a basic description, add additional scientific detail and then contrast behaviour in deep water versus near the shore.

Given Data / Assumptions:

• P notes that tsunamis move throughout the depth of the ocean, not just on the surface.
• Q says that a tsunami wave is not much different in height from other ocean waves when in the open ocean.
• R concludes that this is why a tsunami generally goes unnoticed in the open ocean.
• S states that due to its long wavelength, a tsunami piles up when it approaches land.
• We assume the paragraph will explain the deep water behaviour first, then mention why it is not noticed and finally show what happens at the shoreline.

Concept / Approach:
For scientific explanatory passages:

• Introduce the phenomenon with its basic properties (height and motion).
• Explain consequences of those properties in one context (here, the open ocean).
• Then contrast with behaviour in another context (near land).
• Use logical connectors such as "That is why" and "But" to determine sequence.

Here, "That is why" in R must follow a description in Q, and "But" in S signals a contrast with the earlier behaviour described.

Step-by-Step Solution:
Step 1: P can serve as the first sentence because it begins with "In addition" and states a distinctive property: tsunamis move through the full depth of the ocean. Although "In addition" hints at previous context in a longer passage, within this set it nicely introduces a specific physical characteristic. Step 2: Q follows as it adds another basic fact: in terms of height, tsunami waves in the open ocean are not much different from other waves. Together, P and Q give us two physical properties: movement through depth and modest height. Step 3: R naturally comes next because "That is why a tsunami generally goes unnoticed in the open ocean" explains the combined effect of the properties in P and Q. Step 4: S then introduces a contrast with "But", explaining that due to long wavelength, the same wave "piles up" on approaching land, which accounts for the observed destructive height near the shore. Step 5: The order PQRS therefore describes the phenomenon from properties to effects in deep water, then to contrasting behaviour near land.

Verification / Alternative check:
Reading PQRS, the paragraph first provides key properties (depthwise motion and modest height), then uses "That is why" to explain the lack of visibility in open water, and finally contrasts this with shoreline behaviour. Other sequences do not respect the connectors. RSPQ would begin with "That is why", which requires some previous explanation. QSRP would place S "But due to its wavelength..." immediately after Q without explaining why the wave is unnoticed first. SRPQ starts with a contrast "But" even though no earlier behaviour has yet been mentioned, making it logically incomplete.

Why Other Options Are Wrong:

• RSPQ: Opens with a conclusion "That is why", which has nothing to refer back to in the given order.
• QSRP: Jumps from the wave's normal height to piling up near land, and only later tries to explain why it is unnoticed, which breaks the logical order.
• SRPQ: Begins with "But", signalling contrast, yet does not have any previous statement in the set to contrast with.

Common Pitfalls:
Students often ignore discourse markers such as "That is why" and "But", which are strong indicators of relative position in a paragraph. Another pitfall is to think any scientifically sounding sentence can start the paragraph even if it clearly depends on earlier information. In such questions, always align cause with effect and make sure explanations come after the facts they explain, not before.

Final Answer:
The correct order of the parts is PQRS, so the correct option is PQRS.