Solution:(a) Gordon Hearn contributed significantly to the understanding of social group work through her work on 'Theory Building in Social Work'.
(b) Wilson and Ryland focused on practical aspects of group work in their book, 'Social Group Work Practice'.
(c) Harleigh Trecker's Social Group Work Principles and Practice is foundational in outlining principles of group dynamics and social interventions.
(d) Gisela Konopka emphasized therapeutic approaches in working with children in groups.