Concept:Living organisms may be unicellular (single-celled) or multicellular. A single-celled organism performs all life functions within one cell.
Explanation:- Option D: Paramecium is a unicellular protozoan, clearly single-celled.
- Option A: A hen's egg is a single cell before fertilization and remains single-celled initially.
- Option B: A zygote is the single cell formed by fusion of gametes, thus unicellular.
- Option C: An embryo develops from the zygote by repeated cell division; it consists of many cells, so it is multicellular.
Therefore, the only one that is not single-celled is the embryo.
Answer:C. embryo