In this task, you need to count the number of nouns/verbs in the given sentence.

Example Input: Sentence: 'A polar bear stands on a rock surface in a zoo'. Count the number of verbs in this sentence.
Example Output: 1

Example Input: Sentence: 'A person holding a bottle while riding a skateboard'. Count the number of verbs in this sentence.
Example Output: 2

Example Input: Sentence: 'A duck is walking on the ground beside some ferns'. Count the number of verbs in this sentence.
Example Output:
1