What is measured when calculating velocity during an agile sprint?

What is measured when calculating velocity during an agile sprint?

• Number of tasks
• Person-hours
• Any of the answers
• Story points 

EXPLANATION

Calculation of Velocity

The first version is actual velocity and involves dividing the total number of story points completed by the number of sprints. For example, if the development team has completed a total of 70 points over two sprints, the team's actual velocity would be 35 points per sprint.
Velocity is a measure of the amount of work a Team can tackle during a single Sprint and is the key metric in Scrum. Velocity is calculated at the end of the Sprint by totaling the Points for all fully completed User Stories.