Usability is the quality factor that measures the degree to which a system can be used by specified users to achieve goals with effectiveness, efficiency, and satisfaction. The description in the question—"the effort required to learn, operate, prepare input, and interpret output"—directly aligns with the core components of usability. Specifically, it combines the concepts of learnability (ease of learning) and operability (ease of control and operation), which are internationally recognized sub-characteristics of the main usability attribute as defined in software quality models like ISO/IEC 25010.

A. Trainability: This is a sub-characteristic of maintainability, referring to the ease of training new maintenance personnel, not end-users' operational effort.

B. Testability: This quality attribute relates to the effort needed for testing the software to ensure it is defect-free, not the end-user's interaction with the system.

D. Transferability: This is a sub-characteristic of portability, describing the ease with which software can be moved from one hardware or software environment to another.

1. International Organization for Standardization (ISO). (2011). ISO/IEC 25010:2011 Systems and software engineering — Systems and software Quality Requirements and Evaluation (SQuaRE) — System and software quality models. Section 4.2.3, "Usability," defines the characteristic and its sub-characteristics, including "Learnability" (effort to learn) and "Operability" (effort to operate and control).

2. Miguel, J. P., Mauricio, D., & Rodríguez, G. (2014). A Review of Software Quality Models for the Evaluation of Software Products. International Journal of Software Engineering & Applications, 5(6), 31-53. https://doi.org/10.5121/ijsea.2014.5603. (This paper reviews various quality models, including ISO/IEC 25010, and on page 38, Table 2 explicitly defines Usability and its sub-characteristics, aligning with the question's description).

3. University of Victoria. (n.d.). SENG 426: Software Quality Engineering - Lecture 03: Software Quality Attributes. Courseware. Retrieved from https://www.ece.uvic.ca/~daler/seng426/lectures/03-Quality-Attributes.pdf. (Slide 13 of this university lecture presentation defines Usability as "The capability of the software product to be understood, learned, used and attractive to the user," which directly supports the correct answer).