To determine the force in member BD of the truss, we apply the method of sections, which allows us to cut the truss through three members and consider the equilibrium of one of the resulting sections.

In this case, we pass a section through members BD, CD, and CE. To apply this method effectively, it is essential to take moments about a joint that is not intersected by the section. The best choice in this scenario is joint C because it is directly connected to the members cut by the section, and using it will eliminate the forces at other joints in the calculation.

Let's verify why joint C is the correct choice:

1. Joint A: If we take moments around joint A, we would still have to deal with forces in members AC and AB, making the calculation complex.
2. Joint B: Taking moments about joint B would include the forces in members BA and BC, both unaffected by the section.
3. Joint C (Correct Choice): Taking moments about joint C simplifies calculations as the moments will directly relate to forces in BD, CD, and CE, hence directly solving for the interest member BD.
4. Joint D: Similarly, joint D will involve unnecessary complexity due to interactions at the supports and other members.

Thus, taking moments about joint C allows us to focus on the internal forces in the members directly cut by the section, simplifying the analysis and solution for the force in BD.

By performing the equilibrium analysis about joint C, calculate as follows:

Summing moments about joint C:

This allows us to solve for the unknown force in BD directly.

Conclusion: The correct choice for simplifying the calculation of force in member BD via the section method is joint C.