The organism among the options provided that can reproduce both sexually and asexually is the protist.
Many protists, such as certain types of algae and protozoa, have the capability to reproduce through both asexual methods (like binary fission or budding) and sexual methods (such as conjugation or gamete fusion).
In contrast, dogs and sandhill cranes primarily reproduce sexually, while starfish can also reproduce asexually through methods like regeneration, but their primary mode is usually sexual reproduction.