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

Example Input: Sentence: 'a cat is standing on a green bench looking on'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 2

Example Input: Sentence: 'a flat screen tv sitting in the corner of a living room next to a pumpkin'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'a bunch of zebras are standing in a pin together'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
2