7. Which is the correct ordering of the structure types for the material structures shown in the following figure? (a) a-Single crystal, b-single crystal, c-polycrystal, d-amorphous (b) a-Polycrystal, b-single crystal, c-amorphous, d-amorphous (c) a-Single crystal, b-single crystal, c-amorphous, d-polycrystal (d) a-Amorphous, b-single crystal, c-amorphous, d-polycrystal (e) a-Polycrystal, b-single crystal, c-amorphous d-polycrystal (a) (b) (c) (d)