It wants you to explain why its a chemical change. Signs of chemical changes are formation of gas bubbles, cloudyness, change in color or odor.
Fossil evidence, and biographical evidence.
They're celled subsistence farmers, their farming practice is subsistence farming, where most of the product they grew or reared are for themselves and their families, they usually don't take the products to the markets for commercial purposes, instead those who do that are practising commercial farming.
The best answer is D.
The mass number of an element is the sum of the number of protons and the number of neutrons. Protons and neutrons both weigh about one atomic mass unit or amu.
The nucleus of an atom is made up of protons and neutrons. Both these two types of particles are almost the same size. Almost all the mass of an atom (99%) is in the nucleus. Atomic mass therefore is really a measure of the size of the nucleus.
