Final answer:
The best word to complete the sentence is 'vast'. It means extremely large or wide-ranging.
Step-by-step explanation:
The best word to complete the sentence is vast.
The word 'vast' means extremely large or wide-ranging. In the given sentence, 'vast knowledge' signifies a wide range of knowledge on the subject.
For example: because the questions referenced a variety of topics, my vast knowledge on the subject came in handy when completing the test.