单项选择题

Three passions, simple but very strong, have governed my life: the longing for love, the search for knowledge, and sympathy for the suffering of mankind. These passions, like great winds, have blown me back and forth, accompanying me through my life, making me suffering with anxiety and despair.
I have sought love, first, because it brings such uncontrolled feelings that I would often have sacrificed all the rest of life for a few hours of this joy. I have sought it, next, because it relieves my loneliness that I would follow it all the way. I have sought it, finally, because in the union of love I have seen the vision of the heaven that poets have imagined. This is what -- at last -- I have found.
With equal passion I have sought knowledge. I have wished to understand the hearts of men. I have wished to know why the stars shine. And I have tried to understand the world around me. A little of this, but not much, I have achieved.
Love and knowledge, so far as they were possible, led upward toward the heavens. But always pity brought me back to earth. Cries of pain re - echo in my heart. Children in famine, victims tortured by oppressors, poverty, and pain make a mockery of what human life should be. I long to wipe out the evil, but I cannot, and I too suffer.
This has been my life. I have found it worth living, and would gladly live it again if the chance were offered me.

The writer thought his life worth living probably because（）

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