Hint: The term microscopic refers to any tiny substance or organism. So microscopic plants refer to plants which consist of a single cell. Microscopic plants are also known as phytoplankton.
Complete answer: Algae are single celled mostly aquatic organisms. They belong to the kingdom Protista. The size of algae is microscopic and hence referred to as microscopic plants. The fact that they are considered as plants is due to the presence of green color pigment called chlorophyll. With the help of this pigment they can produce their own food by a process known as photosynthesis. Hence they are called microscopic plants. However, unlike plants their body is not differentiated into parts such as stem, roots, and leaves. Algae are also called phytoplankton. They depend on the sunlight for their growth. The word phytoplankton usually refers to marine algae.
So, option A is the correct option.
The word fungi refers to the eukaryotic organisms which includes microorganisms like yeast, mushroom and mold. Fungi do not produce their own food. Therefore, they are called heterotrophs. Bacteria is a type of prokaryotic cell. The shape and size of bacterial cell varies from minute spheres, spiral threads and cylinders, to filamentous chains and flagellated rods. They are microscopic in nature and are found everywhere on earth.
Note: Phytoplankton can be considered as the pasture of the sea. They provide energy and food for the other living aquatic organisms in the ocean. Some species of phytoplankton are toxic. The size of algae varies from 0.0001 mm to 0.25 mm. Cyanobacteria is an example of phytoplankton.