S, M, E and F are working in shifts in a term to finish a project. M works with twice the efficiency of others but for half as many days as E worked. S and M have 6 hour shifts in a day, where E and F have 12 hours shifts. What is the ratio of contribution of M to contribution of E in the project?
(a) 1:1 (b) 1:2
(c) 1:4 (d) 2:1