The project manager is briefing management on project status and identifies a negative schedule variance but a positive cost variance. Which of the following conclusion is reasonable?
A、The project is behind schedule but may be brought back on schedule by adding resource
B、The project is ahead of schedule but over budget and needs further investigation
C、The project is behind schedule, over budget and merits serious concern
D、The project is ahead of schedule, under budget and progressing with no obvious issues