Answer (C)
Following will be distance vectors of all nodes.
Shortest Distances from $R_1$ to $R_2, R_3, R_4, R_5\ and\ R_6$
$R_1 (5, 3, 12, 12, 16)$
Links used$:R_1-R_3, R_3-R_2, R_2-R_4, R_3-R_5, R_5-R_6$
Shortest Distances from $R_2$ to $R_3, R_4, R_5\ and\ R_6$
$R_2 (2, 7, 8, 12)$
Links used$: R_2-R_3, R_2-R_4, R_4-R_5, R_5-R_6$
Shortest Distances from $R_3$ to $R_4, R_5$ and $R_6$
$R_3(9, 9, 13)$
Links used$:R_3-R_2, R_2-R_4, R_3-R_5, R_5-R_6$
Shortest Distances from $R_4$ to $R_5$ and $R_6$
$R_4 (1, 5)$
Links used$:R_4-R_5, R_5-R_6$
Shortest Distance from $R_5 to R_6$
$R_5$ (4)
Links Used: $R_5-R_6$
If we mark, all the used links one by one, we can see that following links are never used.
$R_1-R_2$
$R_4-R_6$