What action did Pat take on the race?

The action that Pat took on the race can be identified more conclusively by understanding the context in which the actions provided are typically performed regarding a race. "Betting" on a race implies a level of engagement with the event that indicates an interest in the outcome, suggesting that Pat was involved in a way that didn't require physical participation, such as running or walking.

When someone bets on a race, they are often analyzing the participants' abilities and making a choice based on strategy, luck, or information. This action does not necessitate physical exertion like walking or running, nor does it imply a passive role like simply watching the event unfold. Therefore, "Bet" is the most appropriate choice, as it illustrates a committed involvement in the race beyond mere observation.

The other actions, while related to a race, do not convey the level of decision-making that betting involves. Walking and running suggest physical participation, while watching indicates passive observation, neither of which capture the active decision-making role implied by placing a bet.