Option 1 -> Creates grammatically incorrect flow starting with "endangered species need legal protection shrinking habitats..."
Option 2 -> Starting with "both plants and animals and if they are to survive..." makes no grammatical sense.
Option 3 -> Forms coherent sentence: "Shrinking habitats are a threat to both plants and animals and endangered species need legal protection if they are to survive."
Option 4 -> Poor structure with "endangered species need legal protection shrinking habitats are a threat to..."
Hence, Option 3: (B), (D), (A), (C) -> The sentence logically begins by identifying the problem (shrinking habitats threatening plants and animals), then presents the solution (legal protection for endangered species), and concludes with the condition (if they are to survive). This creates a clear cause-effect-condition relationship. -> correct