Which condition is to be met for occurrence of stagnation point on a conical surface at an angle of attack with free stream? (Vθ, Vϕ are cross flow velocities)

Which condition is to be met for occurrence of stagnation point on a c

1.	Which condition is to be met for occurrence of stagnation point on a conical surface at an angle of attack with free stream? (Vθ, Vϕ are cross flow velocities)
A.	Vθ + Vϕ = 1
B.	Vθ + Vϕ = 0
C.	Vθ2 + Vϕ2 = 0
D.	(Vθ + Vϕ)2 = 1
Answer» D.