Progressive Duets Volume 1 Cello ( Easy to Medium ) Is a comprehensive publication of two volumes of graded duets that have been arranged or composed by Clark and Gazda. Playing duets is an excellent way for the student to build emsemble skills with colleagues or teachers, It is published for violin, viola, cello and bass, and is arranged so that it can be performed by any two of these string instruments, making the collection a valuable tool in the school classroom as well.