Unit that cannot be used to express volume

Will you chech and finish these for me, because i am stumped with them.

The focal length of a relaxed human eye is approximately 1.7 cm. when we focus our eyes on a close up object, we can change the refractive power of the eye by about 16 diopters. (a) does the refractive power of our eyes increase or decrease by 16 diopters when we focus closely? explain. (b) calculate the focal length of the eye when we focus closely.

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?