Final answer:
D. Diatoms are the microscopic, single-celled floating algae that contribute to biogenous sediment by forming glassy cell walls that accumulate after death.
Step-by-step explanation:
The microscopic, single-celled floating algae that accumulate to form biogenous sediment are known as D. diatoms.
These unicellular photosynthetic protists encase themselves in glassy cell walls composed of silicon dioxide.
They are a key component of freshwater and marine plankton and can reproduce both sexually and asexually.
Diatoms can also form colonies, which may create a biofilm on surfaces, and their dead remains contribute to sedimentary rock known as diatomaceous earth, which is used for various industrial purposes.