What can be said about prokaryotes and eukaroytes?
a. prokaryotes always have a nucleus, but eukaryotes don't.
b. both of these cell types contain a nucleus.
c. eukaryotes always have a cell membrane, but prokaryotes don't.
d. both of these cell types contain genetic material.

Eukaryotes always have a cell membrane, but prokaryotes don't. Eukaryotic and Prokaryotic cells are both building blocks of life in different organisms. The main difference of two is in its structures. Eukaryotic cells contain organelles that are found inside membranes, like the nucleus, which stores chromosomes and DNA. Prokaryotic cells don't have a nucleus and no true chromosomes. Prokaryotic cells are unicellular while eukaryotes are multicellular. The presence of mitochondria, chloroplasts, and cell wall are all distinct to Eukaryotic cells. Eukaryotic cells are found in animals and plants, while bacteria and archaea have prokaryotic cells.  

In terms of existence, prokaryotes have been on Earth for millions of years; while eukrayotic cells have come to existence through the process of evolution.