In English, a clause is a sentence component that contains a subject and a predicate. Which of the following options correctly describe the structural characteristics of a clause?

A、A clause can stand alone as a sentence, expressing a complete meaning.
B、A clause is usually introduced by a connecting word, such as 'that' or 'because'.
C、A clause must contain a subject and a predicate.
D、The subject and predicate of a clause can be omitted.
E、A clause can function as part of a main clause, serving different grammatical functions.