Q.Animals that can move from Fresh water to Sea water :

A straight diagonal line (internal level tracking external level exactly) represents a conformer; a curve plateauing at the ideal reference level represents a full regulator; a curve plateauing just below that represents a partial regulator.

Organisms respond to changes in abiotic (external) conditions in different ways, conventionally shown on a graph of internal physiological level against external environmental level. A conformer's internal level simply tracks the external level throughout the range shown -- graphically this is a straight, unbroken diagonal line, matching curve A in the figure, since the organism does not regulate its internal environment at all and instead lets it change directly with the surroundings (e.g., many aquatic invertebrates are thermoconformers). A regulator, by contrast, uses homeostatic mechanisms to actively maintain its internal environment relatively constant despite changes in the external environment, at least within tolerable limits -- graphically this shows an initial rise (before regulation is fully effective) followed by a plateau at a …

Catadromous fishes migrate from freshwater habitats to the sea to breed.

Some fish species undertake long-distance migrations between freshwater and marine habitats for breeding, a behaviour called diadromy. Catadromous fishes, such as the freshwater eel (Anguilla), live and grow in rivers and lakes (fresh water) but migrate to the sea to spawn, matching the movement described ('fresh water to sea water'). Option (c) Anadromous fishes show the opposite pattern — they live in the sea but migrate into freshwater rivers to breed, as seen in salmon. Options (b) Stenother …

Migration is the adaptation by which organisms move to a more favourable habitat to escape seasonal shortage of food and water.

Many animals (e.g. migratory birds, wildebeest, some fish) undertake long-distance migration to escape unfavourable conditions -- including scarcity of food and water -- in their home range, moving to areas with better resource availability and returning when conditions improve; this directly overcomes food/water scarcity by relocating rather than enduring it in place. A short reproductive period (a) affects breeding timing, not resource scarcity directly. Winter sleep/hibernation (b) is an adaptation to escape cold temperatures (and indirect food scarcity in winter) by lowering metabolism and remaining dormant in one place, not by seeking food/water elsewhere. Summer sleep/aestivation (d) s …