Convergent adaptation refers to different kinds of organisms with relatively distant ties. Because they live in the same or similar environment for a long time and accept the same ecological environment choice, only the types that can adapt to the environment can be preserved. Convergent adaptation refers to the same type of adaptation. Such organisms, such as living under different conditions for a long time, will show significant differences in appearance, habits and physiological characteristics in order to adapt to their environment. According to the above definitions, Which of the following are convergent adaptations:. ['Castor is an annual herb in the north of China, but a tree-like perennial in the south.', 'The faeces of herbivorous fish can promote the breeding of stingrays. For filter-feeding fish such as sturgeon and sturgeon, the water quality can be cleared, which is beneficial to the life of herbivorous fish.', 'Polar bears evolved from brown bears. The leather coat is white and the same color as the Arctic environment, which is conducive to predation. The shoulders are streamlined and the feet have bristle, which allows them to walk on ice without slipping.', 'Mammalian whales, dolphins, walruses, seals, sharks of fish, they are all far apart in kinship, but all live in the ocean for a long time, and the entire body becomes a spindle shape suitable for swimming.']