`=>` B. were not to hear 

- Sign: In Boston, where he worked by day as a teacher of the deaf, he worked far into the night experimenting with the electrical transmission of the sound.

- the deaf (n): người khiếm thính `->` Người ko thể nghe = people who were not to hear 

1B 

→ Trích dẫn:   In Boston , where he worked by day as a teacher of the deaf, he worked far into the night experimenting with the electrical transmission of the sound . 

→ Vì ở đây theo dịch nghĩa the deaf = were not able to hear ( = người điếc, người không thể nghe đc)

Học tốt!!!