Usually when the word begins with a vowel. Here are some examples.
I bought a pear.
I bought an apple.
Could have had a V8
Could have had an asparagus
Yes but if you are in school and you have to do this for homework... (possibly) then they might want you to use a better word instead of something that is used as a describing word everyday. For example, just use "Amazing" or "Gorgeous" I usually don't hear those words everyday, I only hear "Nice" so yes "Nice" is a describing word but maybe you could go with something else more creative, like a word that is not often used. But it's your choice!
You say is when describing a single object or person. Are is used for describing multiple objects or people. Ex: The apple is on the table. Ex: The apples are on the table.
To show possession
Mine as in describing an actual mine (ie coal mine) is a noun because it is a thing. Mine as in the action "to mine something" is a verb. It can also be used as a pronoun when describing something belonging to oneself.
How dangerous something is! It's jargon, a term usually used for describing the seriousness of a disease.
The word 'my' is first person, an adjective describing something belonging to the speaker. My is not ever used in the second person.
Something describing a noun.
"Elegant" is a descriptive term that conveys a sense of grace, style, and sophistication in describing something or someone.
Both "resistance against" and "resistance to" are commonly used and generally correct. "Resistance against" is often used when describing something actively opposing or fighting against resistance, while "resistance to" is used when describing something's ability to withstand or endure resistance. Both phrases can be correct depending on the context in which they are used.
It can be used as a noun for example the animal or as an adjective like describing something big or large
Rehabilitation is used more for describing the restoring of a person to good health. Reconstruction is used to describe the rebuilding of something.
"Animalistic" is the term used to describe something as having qualities or characteristics associated with animals.