Endocrinology is a part of medicine that has to do with hormones and endocrine gland, people who work in that part are called "endocrinologists".
The use of a, an, or the is a signal that a noun is coming.
In the English language, only nouns are preceded by articles. A is used when a noun starts with a consonant (a book, a table, a bottle); an is used when the noun starts with a vowel (an apple, an umbrella, an avocado); the is used when you are referring to a particular thing (The boy I just met is called Mark.)
(I don't know #1) but Romeo's motive for not wanting to fight Tybalt, is because he know's he's on bad terms with the montagues.
