Chinesse poetry is good at using（）to display imagery
A. blank space
B. euphemism
C. brush
D. implication
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Which of the following assertions for the descent direction is incorrect（）
A. The value of the cost function will decrease along the descent direction
B. For an unconstrained optimization problem,there is no descent direction on the local minimizer of the cost function
C. When one uses the descent direction to construct a iteration algorithm, the step size should be sufficiently large
D. In an optimization problem, the descent direction might not be a feasible direction
If the primal LP problem has optimal solutions, then（）
A. The dual problem is bounded
B. The feasible region of the dual problem is nonempty
C. The dual problem has an optimal basic feasible solution
D. The dual problem is non-degenerate
Which of the following assertions for the feasible region of a standard LP problem is incorrect（）
A. The feasible region is convex
B. The feasible region might not have vertex
C. The feasible region might have infinitely many vertices
D. The feasible region might be unbounded
点的水平投影到OX轴的距离等于点的侧面投影到的距离（）
A. OY轴
B. OZ轴
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