GRE Text Completion: ETS Fundamental-GRE填空ETS基础 - VDK7BCV0Z_66H470X

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