Hi I am stuck on this problems

Given a constraint graph as shown. There are seven variables and the value domain is {R, G,B}. At the beginning of solving this CSP, if the assignments are {WA=R,Q=B} and forward checking is deployed, then when the arc consistency algorithm is firstly examining arc NSW-->SA, after that what is the NSW's domain? a. {R,G,B} b. {G,B} c. {R,B} d. {R,G}