please explain

b) Choose the correct time-phased product structure. b) Choose the correct time-phased product structure

The demand for subassembly S is 100 units in week 7. Each unit of S requires 2 units of T and 1 unit of U. Each unit of T requires 1 unit of V, 2 units of W, and 2 units of X. Finally, each unit of U requires 1 unit of Y and 2 units of Z. One firm manufactures all items. It takes 2 weeks to make S, 1 week to make T, 2 weeks to make U, 2 weeks to make V, 3 weeks to make W, 2 weeks to make X, 2 weeks to make Y, and 1 week to make Z. a) Choose the correct product structure. (2) Level 2 Level 2 (2) 2 2 w (2) w (2) (2) b) Choose the correct time-phased product structure. 123 4 Time in weeks 7 T 123456 Time in weeks w 7 123456 Time in weeks 7 123 4 Time in weeks 7