Three particles of equal mass m are situated at verticles of a equilateral triangle of side l. What should be velocity of each particle so that they move on a circular path without changing l

Question

$$(a)\;\sqrt {\frac{GM}{2l}} \quad (b)\;\sqrt {\frac{GM}{l}} \quad (c)\;\sqrt {\frac{2GM}{l}} \quad (d)\;\sqrt {\frac{GM}{3l}}$$