Two long straight wires are connected by a circular section that has a radius `r` as shown in the figure
. All segments of the wire lie in the same plane and carry steady current `I`. The magnetic field at centre O of the circular segment is

Options

A. `(mu0I)/(4 pi r)`
B. `(beta mu0I)/(4 pi r)`
C. `(beta mu0I)/r`
D. `(beta mu0I)/(2 pi r)`.