Evaluate log_6( log_5(15625) ).

Introduction / Context:
This tests composition of logs with different bases. Simplify the inner logarithm first by recognizing perfect powers, then apply the outer logarithm.

Given Data / Assumptions:
15625 is a power of 5.

Concept / Approach:
Compute t = log_5(15625). Since 15625 = 5^6, t = 6. Then evaluate log_6(6) = 1.

Step-by-Step Solution:

Why Other Options Are Wrong:
2 or 3 result from misidentifying the power of 5 or misapplying the outer log.

Final Answer:
1