题干

如图所示,,卷扬机的绳索通过定滑轮用力F拉位于粗糙斜面上的木箱,  使之沿斜面加速向上移动。在移动过程中,下列说法正确的是  

A:F对木箱做的功等于木箱增加的机械能与木箱克服摩擦力所做的功之和

B:F对木箱做的功等于木箱克服摩擦力和克服重力所做的功之和

C:木箱克服重力做的功大于木箱增加的重力势能

D:F对木箱做的功等于木箱增加的动能与木箱克服摩擦力所做的功之和

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A

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    Would it surprise you to learn that, like animals, trees communicate with each other and pass on their wealth to the next generation?

    UBC Professor Simard explains how trees are much more complex than most of us ever imagined. Although Charles Darwin thought that trees are competing for survival of the fittest, Simard shows just how wrong he was. In fact, the opposite is true: trees survive through their cooperation and support, passing around necessary nutrition “depending on who needs it”.

    Nitrogen (氮) and carbon are shared through miles of underground fungi (真菌) networks, making sure that all trees in the forest ecological system give and receive just the right amount to keep them all healthy. This hidden system works in a very similar way to the networks of neurons (神经元) in our brains, and when one tree is destroyed, it affects all.
     Simard talks about “mother trees”, usually the largest and oldest plants on which all other trees depend. She explains how dying trees pass on the wealth to the next generation, transporting important minerals to young trees so they may continue to grow. When humans cut down “mother trees” with no awareness of these highly complex “tree societies” or the networks on which they feed, we are reducing the chances of survival for the entire forest
   “We didn't take any notice of it.” Simard says sadly. “Dying trees move nutrition into the young trees before dying, but we never give them chance.” If we could put across the message to the forestry industry, we could make a huge difference towards our environmental protection efforts for the future.