— Dad, can we go to the shop?I want to buy some sweets.

— _______.Can't you see I'm busy at the moment?[ ]

A. Take it easy        

B. No problem      

C. Forget it          

D. Don't mention it

运输问题是一种特殊的线性规划模型，因而求解结果也可能出现下列四种情况之一：有惟一最优解，有无穷多最优解，无界解，无可行解。