Domain means all the x-values include in the graph.
In this case the graph starts including x-values at 0 and all x-values that are greater then 0.
In other words x can be zero or anything larger
Technically you would show this like so:
x ≥ 0
You use the inequality symbol with the bar underneath because you want to show that 0 is included in the domain. It faces away from the zero and towards the x because x can be larger then 0 not smaller.
I guess in this case you wouldn't be including 0 so your answer is:
B. x > 0
Hope this helped!
~Just a girl in love with Shawn Mendes