湛江雅思培训：雅思7Test1Reading One5

5.定位词：early military echolocation

文章中对应点：D段：

After this technique had been invented, it was only a matter of time before weapons designers adapted it for the detection of submarines.

Both sides in the Second World War relied heavily on these devices, under such codenames as Asdic (British) and Sonar (American), as well as Radar (American) or RDF(British), which uses radio echoes rather than sound echoes.

第二次世界大战可以对应early一词。