Flexibility is the ability to move joints effectively through a complete range of motion. Stretching exercises to lengthen the muscles are exercises for improving flexibility.
There is no universally accepted standard of flexibility that you should compare yourself against. This makes the correct answer D: There is no absolute measure of flexibility.
The correct answer is there is no absolute measure of flexibility.
There is no accepted standard of flexibility. There are US and international health related tests and exams that have items in them that are used to measure flexibility but there isn't a standard that they are set against.