One of the elements of success according to the Shiva Samhita is not included in the options provided, which is option 'C' - Sacrifice.

The Shiva Samhita is a classical text on yoga that outlines various principles and practices for achieving spiritual enlightenment. It emphasizes the importance of discipline, self-control, and inner transformation. The elements of success mentioned in the Shiva Samhita are as follows:

1. Firm belief (a) - Having a strong conviction and faith in the teachings and practices of yoga is considered essential for success. It helps in maintaining focus, determination, and perseverance on the path of self-realization.

2. Restraint of sense organs (b) - The Shiva Samhita stresses the importance of controlling the senses and disciplining the mind. By restraining the sense organs from being excessively attached to external objects and sensory pleasures, one can develop inner stillness and concentration.

3. Mitahara (d) - Mitahara refers to the practice of moderate and balanced eating. According to the Shiva Samhita, a yogi should consume food that is pure, simple, and nourishing. Overeating or indulging in unhealthy food is discouraged as it can create disturbances in the body and mind.

4. Sacrifice (not mentioned) - The element of sacrifice is not specifically mentioned in the context of success in the Shiva Samhita. Sacrifice, in a spiritual sense, often refers to letting go of attachments, ego, and desires. It involves surrendering one's personal interests and dedicating oneself to a higher purpose or spiritual path. While sacrifice may be considered an important aspect of spiritual growth, it is not explicitly listed as one of the elements of success in the Shiva Samhita.

In conclusion, according to the Shiva Samhita, the element of success that is not included in the options provided is sacrifice (option 'C'). The Shiva Samhita emphasizes firm belief, restraint of sense organs, and moderation in eating as essential elements for achieving success in the path of yoga and spiritual enlightenment.