The answer is: D. The four noble truth
The four noble truth in Buddhist's teachings includes the truth of suffering, the truth of what causing the suffering, the truth of the paths that leading up to the end of the suffering, and the truth of what can end the suffering.
According to the teachings, Individuals need to understand and embodied each part of these truths in order to get rid of the suffering and No one would be able to be liberated unless they understand these 4 noble truths.