Answer:
The correct answer is option c. "cell interactions".
Step-by-step explanation:
Cell-to-cell interactions, or only cells interactions, refers to the mechanisms that cells have to communicate among them. These mechanisms takes place at the surface of the cells by sending and receiving signals in receptors, which later initiate transduction pathways. Cell interactions play a crucial role in the development of embryos, therefore if a knockout mouse has embryonic lethality due to a disruption in a receptor, it is very likely that the development process that is affected is related with cell interactions.