Which of the following statements is/are correct? a. The scale that is used to measure the object must be greater than the length of the object. b. The two devices that can be used to measure length are: Metre scale and Screw gauge. c. All periodic motions are oscillatory and all oscillatory motions are periodic.

All these are correct statements. The scale that is used to measure the object must be greater than the length of the object. The two devices that can be used to measure length are: Metre scale and Screw gauge. In oscillatory motion a body repeats its action in equal interval of time so, all periodic motions are oscillatory motion and vice versa.