Correct Answer: 2 (d, b, a, c) To solve "Sentence Rearrangement" or "Para-jumble" tasks, look for the logical flow of ideas: Step 1 (Introduction): Sentence (d) serves as the best introductory sentence. It defines dark matter and quantifies its estimated presence in the universe, setting the stage for further discussion. Step 2 (Elaboration): Sentence (b) logically follows (d). It explains *why* the concept of dark matter was hypothesized, addressing the observational problems it seeks to resolve. This connects directly to the "mysterious" nature introduced in (d). Step 3 (Secondary Factor): Sentence (a) further elaborates on dark matter's nature, specifically its lack of interaction with light, which is a direct consequence of the issues presented in (b) and explains *why* it remains unseen despite its gravitational effects. Step 4 (Conclusion/Result): Sentence (c) provides a concluding thought. The word "Consequently" signals a result or implication, linking the mysterious existence and elusive properties of dark matter to its fundamental importance for cosmology and the ongoing scientific efforts to understand it.