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

Example Input: Sentence: 'a person jumping in the air on a skateboard'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 2

Example Input: Sentence: 'a black horse standing on a hill top with a white horse'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'a girl using a mobile device sits on the lap of a man in a military uniform'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
4