B

    I have a twin brother, Bob. He is taller than me. His hair is shorter than mine. Many people think we must have many things in common. But in fact this is not true. Bob is more outgoing than me. When my parents' friends come to our house, Bob often sits there and talks to them. But I often sit there and say nothing. Bob likes reading, cooking and drawing. I just like swimming and playing basketball. He has more hobbies than me, but he is not as athletic(擅长运动的) as me. Because Bob does better than me at school, my mom often says to me, “Bob is younger than you, but he can get better grades, you should learn from him.” We both like eating fast food and listening to music.

设变量$x,y$满足约束条件$\left\{\begin{array}{c}y\ge 0\\ x-y+1\ge 0\\ x+y-3\le 0\end{array}\right.$$\begin{array}{c}\mathrm{}\\ \mathrm{}\mathrm{}\\ \mathrm{}\mathrm{}\end{array}$，则$z=2x+y$的最大值为  (    )

如图所示是检测某一传感器的电路图，这种传感器上标有“6V、1.8W”的字样（该传感器可看作一个纯电阻电器），滑动变阻器上标有“10Ω、1A”的字样，电流表的量程为0～0.6A，电压表的量程为0～3V．求：