如图所示，竖直墙壁两侧固定着两轻质弹簧，水平面光滑，一弹性小球在两弹簧间往复运动，把小球和弹簧视为一个系统，则小球在运动过程中（   ）

抛物线$y^2=2px\left(p>0\right)$的焦点为F，A、B在抛物线上，且$\angle AFB=\frac{\pi }{2}$，弦AB的中点M 在其准线上的射影为N，则$\frac{\left|MN\right|}{\left|AB\right|}$的最大值为（     ）

    Alexis, 17, sat quietly in the passenger seat of her dad's car. She let her eyes lazily scan the landscape for wildlife. Then a deer came into view about 200 yards in front of them. “Dad, there's a deer there!” Alexis said. It was a male deer with sharp antlers (角) on each side of its head.

    As the car moved closer, Alexis saw that the deer's head was bent toward the ground. Then she heard a scream and saw an arm fly up near the deer's head. Alexis realized the deer was attacking a woman. Sue, a 44-year-old mother, had been out for her morning run. The deer followed her and edged closer. “I knew I was in trouble.” Sue says. She went to pick up a stick for self-defense, and the deer charged. It lifted her with its antlers and threw her into the air. Sue could feel blood flew down her leg. Within seconds, the deer had pushed her off the road.

    When Alexis and her father pulled up, the deer was throwing Sue like a doll. Alexis looked into the woman's terrified eyes, and before her father had even stopped the car, the teenager jumped quickly out of the car and ran toward the deer. “I was kicking it to get its attention." she says. Then her father, who had followed his daughter, pushed the deer away from the women.

    Alexis helped Sue into the car and then applied a piece of cloth to Sue's injured leg. “We're going to get you to a hospital.” Alexis said. Then she heard her father shout loudly. He had been knocked to the ground. Alexis took hold of a hammer from the car and ran to where her father lay on his back. She beat the deer's head and neck, but the blows didn't scare it away. “I was losing faith.” she says. “A couple more strikes. Alexis.” said her father. “You can do it.”

    Turning the hammer around, Alexis closed her eyes and beat the deer's neck with all her strength. When she opened her eyes, the deer was running away.

    Alexis got in the driver's seat and sped toward the nearest hospital. After Sue was treated, she tearfully thanked her rescuers. “You expect a teenage girl to get on the phone and call for help,” she says, “not to beat up a deer.”