<span>the application of techniques like mass production
Let's look at the available options and see what makes sense.
the use of heat and open fires for cooking
- This sounds like the discovery of fire and as such it happened a long time before the nineteenth century. Wrong answer.
the application of techniques like mass production
- This one looks promising. We'll take if the other 3 options are just plain silly.
the introduction of earthenware such as clay vessels
- This is more recent than the discovery of fire. But it's still a long time ago. Literally thousands of years BC. So wrong answer.
the discovery of the technique of roasting raw foods
- Another discovery that happened thousands of years ago. So also the wrong answer.
So of the 4 choices, 3 of them happened literally thousands of years ago and so well before the nineteenth century. That leaves only 1 viable choices, so the answer is "the application of techniques like mass production"</span>
