In a previous design, the weight of the discus used in track competition is concentrated in a metal center, but now it is lined with lead around the perimeter, thereby improving stability in fl ight and resulting in longer throws.
(A) In a previous design, the weight of the discus used in track competition is concentrated in a metal center, but now it is
(B) According to a previous design, the weight of the discus used in track competition was concentrated in a metal center, but now it is
(C) Once designed with its weight concentrated in a metal center, the discus used in track competition is now
(D) The discus used in track competition, once designed with its weight concentrated in a metal center, but now
(E) The discus used in track competition was once designed having its weight concentrated in a metal center and now

OA is C.

My questions is on B the OG says "it does not make sense to say that the weight of the discus is lined with lead", why so. The weight is lined with the lead as in adjacent to the lead. Why is this wrong.

However the OG does not mention anything about the opening phrase "According to a previous design". We generally use according to a someone (person) and not something (design), had it said according to the design document it would still be teneable. It sounds awkward to say according to the design.

Any thoughts?