Question

Переделать предложение: When he had proved that his theory was correct, he started studying ways and means of improving the conditions of work in very deep coal-mines. (after)

Answer 1

After proving that his theory was correct, he began studying ways and means to improve the working conditions in very deep coal mines.

Answer 2

After proving that his theory was correct, he embarked on a study of methods to enhance working conditions in extremely deep coal mines.