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

Example Input: Sentence: 'a person is riding a bicycle but there is a train in the background'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'a public bathroom with four toilet stalls and four urinals on the wall'. Count the occurrences of the word 'four' in the given sentence.
Example Output: 2

Example Input: Sentence: 'a child rides a wave on a surfboard'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
3