The correct answers are: Before the invention of the telephone, gossiping required a lot more walking. It takes years of practice to master the violin, but only seconds to annoy your neighbors with it.

We use "the" with singular countable nouns to refer to an invention as a general concept rather than a specific object (e.g., invented the telephone).

We also use "the" when talking about playing musical instruments in a general sense (e.g., master the violin, playing the flute). Leaving the article out (invented telephone, playing flute) is incorrect.