Answer
C = {A} C' = {B, C, D, E, F, G}
C = {A, D} C' = {B, C, E, F, G}
C = {A, D, B} C' = {C, E, F, G}
C = {A, D, B, C} C' = {E, F, G}
C = {A, D, B, C, G} C' = {E, F}
C = {A, D, B, C, G, F} C' = {E}
C = {A, D, B, C, G, F, E} C' = { }
The resulting network is
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Cost = 2 + 1 + 4 + 3 + 3 + 5 = 18 units