By the end of 1931, the technique of dubbing ... sufficiently (perfect). Выберите один ответ:
a. perfected
b. had been perfected
c. was perfected

Question

Английский язык: By the end of 1931, the technique of dubbing ... sufficiently (perfect). Выберите один ответ: a. perfected b. had been perfected c. was perfected

kamilahamidova · Answer

By the end of 1931, the technique of dubbing had been perfected sufficiently....