B. A clause has a subject and a verb, but a phrase does not.
In Grammar, a clause is a set of words (that are related to each other) that contains a subject and its corresponding verb. A clause by itself is a group of words, that express a complete idea. Clauses usually are short, simple sentences. Whereas a phrase doesn't have both a subject and a verb. Hence, clauses are a group of words, that could state ideas independently, as separate sentences having a subject and predicate.
See the following sentence: At the entrance, Peter was waiting for her.
As we can observe, the underlined part could be a sentence by itself. While the words in italics could be removed and as a group they don't constitute a sentence altogether.
