线性规划问题有可行解，则（）
A.必有基可行解
B.必有唯一最优解
C.无基可行解
D.无唯一最优解
参考答案：A
简述教育实验的基本类型。
29. If city noises____from increasing, people___shout to be heard even at the dinner table 20 years from now.
A．are not kept; will have to
B．are not kept; have to
C．do not kept; will have to
D．do not kept; have to
