Explanation

(d)
When two oxygen of each $SiO_{4}^{4 -}\$tetrahedron are shared with others, cyclic or ring structures are obtained. These silicates are known as cyclosilicates or cyclic silicates.
$\left\lbrack Si_{6}O_{18} \right\rbrack^{12 -}\$is an example of cyclosilicate. In this silicate six $SiO_{4}$ tetrahedra linked together.