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