In which stage of the cell cycle does the cell die A) interphase
B) mitosis
C) apoptosis

The short answer is that cell death by apoptosis in various phases of cell cycle depends on the cell-type and inducer/stimulus. Hematopoietic cells can undergo apoptosis at all stages of cell cycle as noted by Bertrand. However, mesenchymal or epithelial cells usually undergo apoptosis at the G1/S or G2/M phase of the cell cycle.

They became more resistant.