The yield strength of a material going through grain size reduction increases by a factor, k multiplied by:(where d is the diameter of grain)

The yield strength of a material going through grain size reduction in

1.	The yield strength of a material going through grain size reduction increases by a factor, k multiplied by:(where d is the diameter of grain)
A.	d<sup>2</sup>
B.	d<sup>1/2</sup>
C.	d<sup>-1/2</sup>
D.	d<sup>-2</sup>
Answer» D. d<sup>-2</sup>