A hanging spring is pulled down and allowed to oscillate up and down. As the spring oscillates, its height above the ground, y in metres, can be modelled by the sinusoidal function: y = a sin(bx +c)+a where x is the time in seconds, after the spring is released In this context, the value of d in the sinusoidal function represents: Select one: O a. the maximum height of the spring O b. the length of time it takes the spring to return to its median height O c the length of time it takes the spring to oscillate up and down O d. the height of the spring above the ground before it is pulled down