for _ in range(int(input())):
    s=list(map(lambda x:0 if x=="W" else 1 if x=="G" else -1,list(input())))
    for i in range(len(s)-1,-1,-1):
    	if s[i]==-1:
    		continue
    	if s[i]!=1:
    		s[-1]=0
    		break
    if s[-1]!=-1:
        print("impossible")
        continue
    for j in range(1,len(s)):
        s[j]+=s[j-1]
    ans="possible"
    if s[-1]!=0 or min(s)<0:
        ans="impossible"
    print(ans)
    del s