Final answer:
The aggregation and activation of pro-apoptotic BH123 proteins (Bax and Bak) are caused by mitochondrial outer membrane permeabilization (MOMP).
Step-by-step explanation:
The correct answer is option b) Mitochondrial outer membrane permeabilization (MOMP). Mitochondrial outer membrane permeabilization (MOMP) causes the aggregation and activation of pro-apoptotic BH123 proteins (Bax and Bak). MOMP refers to the permeabilization of the outer membrane of mitochondria, leading to the release of cytochrome C into the cytoplasm and the activation of apoptosis.