Answer:
B. Two cells, but half the size
Explanation:
Single-celled organisms, which are also referred to as unicellular organisms, usually have a growth mechanism or process known as binary fission.
Binary fission is a an asexual reproduction process that involves the division of a mature parent cell into two identical daughter cells of equal sizes that are almost half of their parents cell.
The sentence that best describes how the single-celled organisms shown in the picture above will look like at the end of the growth period is: "b. Two cells, but half the size"