Oxygenic photosynthetic bacteria perform photosynthesis in a similar manner to plants. They contain light-harvesting pigments, absorb carbon dioxide, and release oxygen. Cyanobacteria or Cyanophyta are the only forms of oxygenic photosynthetic bacteria known to date. There are, however, several species of Cyanobacteria. They are often blue-green in colour and are thought to have contributed to the biodiversity on Earth by helping to convert the Earth’s early oxygen-deficient atmosphere to an oxygen-rich environment. Since Anabaena is a type of Cyanobacteria, the correct answer is A.