What technological advance enabled the allied powers to undermine the threat of german u-boats? atomic bomb b-29 bomber howitzer sonar

The German U-boats was detected through sonar. Allies used sonar to detect submerged warships such as the U-boat, which cannot be seen through eyes. But it can only detect those that are under the waters and not on the surface. 

Bbecause the jim crow laws were made to make voting difficult for african americans