It can be inferred that_________ .

* Hướng dẫn giải

Chọn D
Ta có thông tin: “Research into sound that was reproduced at exactly at the same time as the pictures - called
“synchronized sound” – began soon after the very first films were shown”. Chú ý cụm từ “at the same time” nghĩa là cùng 1 thời điểm.