In early Buddhist art (such as at Sanchi, Bharhut, and Amaravati), the Buddha was not depicted in human form. Instead, sculptors used specific physical symbols to represent his presence and the major events of his life. This is known as the aniconic phase of Buddhist iconography.

• The meditation of the Buddha is represented by the Empty Seat (Vajrasana or Bodhimanda). It is often depicted under a parasol or the Bodhi tree, signifying the exact spot at Bodh Gaya where he sat in deep meditation to attain awakening.
• The Buddha's First Sermon (Dharmachakrapravartana) is symbolized by the Wheel (Dharmachakra), representing the "turning of the wheel of law" at Sarnath.
• The Buddha's Mahaparinibbana (his physical death and final liberation) is represented by the Stupa.
• The Buddha's Mahabhinishkramana (the Great Departure or Renunciation) is represented by a Riderless Horse (Kanthaka), symbolizing Prince Siddhartha leaving his royal palace to seek truth.

Therefore, option A is the correct answer.