Write the formula of power lens.

     The power of a lens is defined as the reciprocal of its focal length in meters, or D = 1/f, where D is the power in diopters and f is the focal length in meters.

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b. latent learning (the word "latent" itself means something that exists but isn't obvious, only under certain conditions! )

answer a fan shaped mass of sediment deposited at the base of a mountain front do to an abrupt change in stream gradient;