n an Agile project, the scrum master is $\_\_\_\_\_\_\_.$

a$.$ an extra helper needed for their specific expertise

b$.$ the project manager who serves and leads in a collaborative, facilitating manner

c$.$ someone who helps the team expand their thinking by focusing on many possibilities or to help them focus on selecting from many options

d$.$ the individual who ensures that the needs and wants of the customer's organization are identified and prioritized