Answer: The correct answer is -
B) bacteria.
Step-by-step explanation:
The first life form on Earth is considered to be a microbe with single-cell, lacking a nucleus and membrane bound subcellular compartments, known as prokaryotes (bacteria).
They seemed to have first appeared around four billion years back, just a few hundred million years after which Earth formed itself.
Thus, scientists believed that the first life forms to appear on planet Earth were similar to bacteria.