Answer
1500 people selected candidate A as their second choice.
Work Step by Step
In the preference table, we can see that 900 people selected the candidates in the order C, A, B. We can also see that 600 people selected the candidates in the order B, A, C. All of these people selected candidate A as their second choice.
Therefore, the number of people who selected candidate A as their second choice is 900 + 600 which is 1500.