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

Example Input: Sentence: 'a pink unicorn painted on a newspaper box across the street from a bus in front of a theater'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 4

Example Input: Sentence: 'a girl riding a bike wth a dog chasing her'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'a pickup truck towing a boat on a trailer'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
3