pk1,pk2,pk3,content
b,a,a,b-a-a
b,b,a,b-b-a
b,c,a,b-c-a
b,d,a,b-d-a
b,e,a,b-e-a
b,f,a,b-f-a
b,g,a,b-g-a
b,h,a,b-h-a
b,i,a,b-i-a
b,j,a,b-j-a
b,k,a,b-k-a
b,l,a,b-l-a
b,m,a,b-m-a