The correct option is A External
Algae are simple without thallus, autotrophic non-vascular plants having unisexual organs and no embryo formation. Algae majorly reproduce by external fertilization. This type of fertilization occurs mostly in wet environments and requires both male and female organisms to release their gametes into their surrounding (usually water). It is seen in the majority of algae as the gametes in algae are fused in water outside the plant body. An advantage of external fertilization is that it results in the production of a large number of offspring. One disadvantage is that environmental hazards such as predators greatly reduce the chance of surviving into adulthood. Amphibians and fish, aquatic algae are examples of animals that reproduce this way.