1-C. Portable audio systems tend to create background noise.Portable audio systems tend to create background noise.
ポータブルオーディオシステムは、傾向がある、バックグラウンドノイズを生成するダヨ。
2-C. Background noise often helps people concentrate on music.Background noise often helps people concentrate on music.
バックグラウンドノイズは、多くの場合、役立ちます、人々が集中するのにダヨ、音楽にダヨ。
3-C. In these settings, music may be partly lost in background noise, making it hard for the listener to concentrate on it.In these settings, music may be partly lost in background noise, making it hard for the listener to concentrate on it.
4-C. There was so much noise in the classroom that Hisako could not make herself heard.There was so much noise in the classroom that Hisako could not make herself heard.