Final answer:
The subject of the sentence 'The cause of the Black Death was unknown in the 1300s.' is 'The cause of the Black Death'.
Step-by-step explanation:
The subject of the sentence 'The cause of the Black Death was unknown in the 1300s.' is 'The cause of the Black Death'. The verb is 'was'. The subject is asking for the identification of the subject(s) in the sentence. In this case, the subject is 'The cause of the Black Death'..
The subject is the noun or pronoun modifying the verb. Usually, it's the entity “performing” the action. The object is the noun or pronoun usually being affected by the actions of the subject.
The subject is who or what the sentence speaks about. The subject will be a noun or pronoun, a word naming a person, place, or thing. The verb is what the sentence says about the subject. The verb might express an action or a state of being (a form of the verb 'to be').
The subject is what (or whom) the sentence is about, while the predicate tells something about the subject. In the following sentences, the predicate is enclosed in braces ({}), while the subject is highlighted. Judy {runs}. Judy and her dog {run on the beach every morning}.