A regular tetrahedron has all its vertices on a sphere of radius $R$. Then the length of each edge of the tetrahedron is (a) $( \sqrt{2} / \sqrt{3} ) R$ (b) $( \sqrt{3} / 2 ) R$ (c) $( 4 / 3 ) R$ (d) $( 2 \sqrt{2} / \sqrt{3} ) R$
A regular tetrahedron has all its vertices on a sphere of radius $R$. Then the length of each edge of the tetrahedron is\\
(a) $( \sqrt{2} / \sqrt{3} ) R$\\
(b) $( \sqrt{3} / 2 ) R$\\
(c) $( 4 / 3 ) R$\\
(d) $( 2 \sqrt{2} / \sqrt{3} ) R$