Step 1: Analyzing the association.
- "Soup" and "Vegetables" are related to food, while "Blood" is a biological term. "Haemoglobin" is the protein in blood that transports oxygen, which connects well with "Blood" in a biological sense. The word "Haemoglobin" is the most appropriate association for all three words. Step 2: Conclusion.
The word that best fits is "Haemoglobin".