Consider the following distance matrix representing the dissimilarities between four objects (A, B, C, and D) in a hierarchical clustering analysis:

      A   B   C   D
A   0.0 5.0 9.0 6.0
B   5.0 0.0 7.0 8.0
C   9.0 7.0 0.0 3.0
D   6.0 8.0 3.0 0.0

If you perform single-linkage hierarchical clustering (also known as the nearest neighbor method) on this data, what is the height at which the clusters {A, B} and {C, D} will be merged?