In this task, you need to count the occurrences of the given word in the given sentence.

Example Input: Sentence: 'a person flying a kite on a busy city street'. Count the occurrences of the word 'on' in the given sentence.
Example Output: 1

Example Input: Sentence: 'a parked silver subway train next to a platform'. Count the occurrences of the word 'next' in the given sentence.
Example Output: 1

Example Input: Sentence: 'a dog catching a frisbee on a baseball field while its owner watches'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
3