Resource leveling is required whenever individual bars in the Resource Histogram extend beyond the maximum allowed hours. Resource leveling can be done by either adding more resources or modifying the schedule. Option (a) reducing scope or (b) extending working hours would be detrimental to the project's success and is not recommended here. Option D schedule compression which can be done through either crashing or fast tracking wouldn't necessarily be helpful. Since specific bars are showing an overflow, it can be best tackled using resource leveling.