What conclusion does the study conducted by Carr et al. (2013) have regarding the application of the Performance Diagnostic Checklist - Human Services (PDC-HS)? a. The PDC-HS can be used to examine the variables that contribute to staff performance problems in education settings. b. The PDC-HS cannot be used to examine the variables that contribute to staff performance problems in education settings. c. The PDC-HS can be used to examine the variables that contribute to staff performance problems in human-service settings. d. The PDC-HS cannot be used to examine the variables that contribute to staff performance problems in human-service settings. e. none of the above