Which of the following musical terms suggests a moderately loud sound level?

The term that suggests a moderately loud sound level is 'mezzo forte.' In musical notation, 'mezzo forte' indicates that the performer should play or sing at a level of dynamic that is moderately loud, providing a balanced intensity that sits between 'piano' (soft) and 'forte' (loud). This term is commonly used in sheet music to guide musicians in achieving the appropriate volume for a passage, contributing to the overall dynamics and emotional expression of the piece.

Each of the other terms mentioned has distinct meanings: 'legato' refers to a smooth and connected manner of playing or singing, without noticeable breaks between notes; 'mezzo piano' indicates a moderately soft sound level, which is softer than 'mezzo forte'; and 'piano' simply means soft. Understanding these distinctions helps musicians interpret musical scores accurately and convey the intended expressions within a work.