如图所示，保持电源电压不变，当开关S由断开到闭合时，下列说法正确的是（    ）

甲灯额定电压为6V，乙灯额定功率为2W，甲、乙两灯的电阻分别为R_甲和R_乙，且R_甲>R_乙，并保持不变，将它们以某种方式连接到电压为U_A的电源上时,两灯均正常发光,将它们以另一种方式连接到电压为U_B的电源上时，乙灯正常发光,甲灯的实际功率为额定功率的4/9，则电源U_A两端的电压为____ V。

    Food is very important. Everyone needs to 1 well if he or she wants to have a strong body. Our minds also need a kind of food.

    This kind of food is 2.We begin to get knowledge even when we are very young. Small children are 3 in everything around them.They learn 4 while they are watching and listening.When they are getting older，they begin to 5 story books，science books...，anything they like.When they find something new，they love to ask questions and 6 to find out the answers.

    What is the best 7 to get knowledge?If we learn 8 ourselves，we will get the most knowledge.If we are 9 getting answers from others and do not ask why，we will never learn well.When we study in the right way，we will learn more and understand 10.

    已而夕阳在山，人影散乱，太守归而宾客从也。树林阴翳，鸣声上下，游人去而禽鸟乐也。然而禽鸟知山林之乐，而不知人之乐；人知从太守游而乐，而不知太守之乐其乐也。醉能同其乐，醒能述以文者，太守也。太守谓谁？庐陵欧阳修也。