The sea was not an_____the diffusion of the windmill; on the contrary, while the concept of the new invention passed quickly from seaport to seaport, it made little headway inland.
A.element in
B.issue in
C.aid to
D.obstacle to
E.promotion of
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The sea was not an_____the diffusion of the windmill; on the contrary, while the concept of the new invention passed quickly from seaport to seaport, it made little headway inland.
A.element in
B.issue in
C.aid to
D.obstacle to
E.promotion of