What are the three primary methods by which algae reproduce?

The correct answer identifies three primary methods of reproduction in algae: cell division, plant fragmentation, and spores.

Cell division, specifically through a process known as mitosis, allows single cells to split and create two identical daughter cells, which is a fundamental reproduction strategy for many algae.

Plant fragmentation refers to a form of asexual reproduction where fragments of the parent algae break off and grow into new individuals. This method is particularly effective in environments where algae can rapidly colonize or spread.

Finally, spore formation is a reproductive strategy utilized by many algal species wherein specialized cells (spores) are produced that can disperse and germinate into new organisms under favorable conditions. This method is essential for the survival and propagation of algae over varying environmental conditions.

The other choices do not accurately reflect this combination required for classifying the primary reproductive strategies of algae.