Final answer:
The word 'challenge' can be used as a noun to mean an interesting or difficult task, and as a verb to mean working together on a difficult task.
Step-by-step explanation:
In excerpt A, 'challenges' is used as a noun and means an interesting or difficult task. For example, 'He enjoys taking on new challenges every day.'
In excerpt B, 'challenge' is used as a verb and means to work together on a difficult task. For example, 'We will challenge ourselves to complete this project.'
Learn more about Parts of speech and meanings of different forms of the word 'challenge'