【正确答案】正确答案：Logical subject is the subject of a sentence that expresses the actual agent of an expressed or implied action. In passive voice such as "John was bitten by a dog", we have two terms "grammatical subject" and "logical subject". Since the core object noun (John in this case) sits in the slot before the verb in the passive, it is called grammatical subject, for the original object noun phrase occupies the grammatical space before a verb, the space that a subject normally occupies; the core subject (A dog), now the object of a preposition (by a dog), is called the logical subject, since semantically the core subject still does what a subject normally does; it performs an action.