Answer:
The correct answer would be b. Their cells are small and lack a nucleus.
Both archaea and bacteria are prokaryotic organisms that is, they both are devoid of a nucleus and other membrane-bound organelles such as mitochondria, chloroplast et cetera.
They also share a similarity in terms of shape and size of the cells. Both of them are unicellular in nature and can not be seen by naked eyes.
They show variations in their genetic and biochemical ways. For example, archae contains three RNA polymerases whereas bacteria contain a single RNA polymerase.
Their cell wall also show variation in composition. For example, a bacterial cell wall contains peptidoglycans, whereas archae cell wall does not.
Thus, we can say that archae and bacteria are similar in a manner that their cells are small and lack a nucleus.
