Conjunction

A conjunction is a word that is used to connect words, phrases, or clauses in a sentence. It helps to establish a relationship between the connected elements. In this case, the word 'but' is used as a conjunction to connect the two independent clauses 'Andy knocked on the door' and 'nobody answered'.

Explanation:

Andy knocked on the door, but nobody answered.

- 'Andy knocked on the door' is the first independent clause in the sentence. It states that Andy performed the action of knocking on the door.
- 'but' is a conjunction that connects the two independent clauses together, indicating a contrast or opposition between the actions in the clauses.
- 'nobody answered' is the second independent clause in the sentence. It indicates that there was no response to Andy's knocking on the door.

The conjunction 'but' is used here to show the contrast between the action of knocking on the door and the lack of response. It helps to convey the idea that despite Andy's action, nobody answered the door.

In this sentence, 'but' is functioning as a coordinating conjunction. Coordinating conjunctions are used to join two independent clauses of equal importance in a sentence. They include words like 'and', 'but', 'or', 'nor', 'so', 'for', and 'yet'. In this case, 'but' is connecting the clauses 'Andy knocked on the door' and 'nobody answered'.

To summarize, the correct answer is option 'C' - conjunction. In the given sentence, 'but' is used as a conjunction to connect the two independent clauses and show a contrast between the actions described in those clauses.