The magnetic field at O due to current in the infinite wire forming a loop as a shown in Fig.
A. `(mu_(0)I)/(4pid)(cosphi_(1)+cosphi_(2))`
B. `(mu_(0))/(4pi)(2I)/d(tan theta_(1)+tan theta_(2))`
C. `(mu_(0))/(4pi)(I)/d(sin phi_(1)+sin phi_(2))`
D. `(mu_(0))/(4pi)(I)/d(cos theta_(1)+cos theta_(2))`