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

Example Input: Sentence: 'a variety of old motorcycles on display in a shop'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 2

Example Input: Sentence: 'a woman is holding a racket and looking in a mirror'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'a herd of cows grazing along a river'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
2