Your organization's test strategy states that it is desirable to use more than one method...

Comprehensive and Detailed In-Depth Explanation:

The ratio-based estimation method relies on historical relationships between development and testing effort.

Using the given 5:3 ratio:

Thus, the correct answer is 270 person-days (D).

(A) and (C) are incorrect as they overestimate the effort.

(B) underestimates the testing effort based on the ratio.

Ratio-based estimation helps allocate resources effectively based on past project data.