In formal writing you would not begin a sentence with because, therefore, the kind of sentence that begins with because is informal.
this type of sentence would be categorized as incomplete
no because then it would be a sentence fragment.
"Because she was sick" is not any type of sentence structure. It is called a sentence fragment.
a fragment
kind is the adjective because it describing the person
'Until the class begins' is not a complete sentence, and therefore it can not be classified. It is a clause, introduced by the conjunction 'until.' 'Until the class begins' is not a complete thought. We're still waiting for the rest of the sentence. Something will or will not happen, take place, be allowed, etc., 'until the class begins.' Without that something being stated, there is not a complete thought. It takes a complete thought to make a sentence. 'The class begins' is a complete sentence. It sounds like an announcement of some kind. It is perhaps a little awkward or stilted, but it is a complete sentence. It expresses a complete thought. Furthermore, it is a declarative sentence. It states a fact.
Yes, the word "Friends" should be capitalized when used as a proper noun or as part of a title, such as in the TV show "Friends." Otherwise, if used as a common noun, it should not be capitalized.
if the word after it begins in a vowel
The dog ran quickly through the park.
My birthday is in September, and I always look forward to celebrating with my friends and family.
The sentence "Are you going to the library?" is an interrogative sentence because it asks a question. It seeks information about the listener's plans to visit the library.
You could have a sentence like: Of the following choices, which would you prefer?