A) Present Market Demand gives a snapshot of the current consumption levels.

B) Export Market Demand helps in understanding the potential in international markets, which can contribute to overall market potential.

C) Future Market Demand is crucial for projecting growth and long-term viability.

Labour Demand (D) and Retailer's Consumption Preferences (E), while important for operational and marketing strategies, are less directly related to estimating overall market potential.

So, option C is the correct answer.