In the following assertions for descent direction, which ones are correct ? ( )
A.
The descent direction is unique when the cost function is strictly convex.
B.
For a unconstrained optimization problem, an descent direction is also a feasible direction.
C.
If the angle between a vector and the gradient direction is greater than 90º,then this vector is a descent direction.
D.
The value of the cost function will decrease along a descent direction.