阅读下面短文，掌握其大意，然后从1～15各题所给的A、B、C和D项中，选出最佳选项。
Life is full of heartaches, joys and many lessons to learn. However, it is up to us to decide how we begin and end it. I 1 believe that every day when we 2up in the morning, we should be 3of the fact that time is slipping away fast and violently like sand in an hourglass(沙漏).
We can choose to free our minds of whatever lies ahead and prevent life from limiting our vision of the future or 4 us from achieving what we are tending to become. Although, the journey of life will not always be5 because at times we will meet many challenges, we should never despair but 6 every moment. Every choice or decision we make should be pursued 7.
Despite the fact that at some point life present to us countless possibilities, it is those challenging times that always 8 us towards realizing our purpose in life and greatness.
Sometimes life's 9can make us feel that the current situation we face conflicts with how we'd like to keep in life. However, it is only if we allow life's challenges to 10our direction and decision that we may never 11 realize our potential. We should not allow life’s challenges to limit our reach for a better future. If we take control of today to our12 by leaving no stone unturned, tomorrow is already reshaped for the better.
Life is always filled with uncertainties. It is on this basis that we should not 13time on small things and with people who take us for granted. We ought to learn from experiences and use them to reset our14and goal in life. This way, we will be better off, more successful. We should never waste any time or 15 and this can only be actualized once we realize that life is full of possibilities.
（单位：牛顿）的作用而处于平衡状态．已知
成
角，且