题目内容：
根据下面材料，回答题：
Looking back on my childhood, I am convinced that naturalists are born and not made. Althoughwe were brought up in the same way, my brothers and sisters soon abandoned their pressed (紧抱的 )flowers and insects. Unlike them, I had no ear for music and languages, I was not an early reader andI could not do mental arithmetic.
Before World War I we spent our summer holidays in Hungary. I have only the dim memory of thehouse we lived in, of my room and my toys. Nor do I recall clearly the large family of grandparents,aunts, uncles and cousins who gathered next door. But I do have a crystal-clear memory of dogs, thefarm animals, the local birds and above all, the insects.
I am a naturalist, not a scientist. I have a strong love of the natural world, and my enthusiasmhas led me into varied investigations. I love discussing my favorite topics and enjoy burning the mid-night oil, reading about other people's observations and discoveries. Then something happens thatbrings these observations together in my conscious mind. Suddenly you fancy you see the answer to theriddle (迷), because it all seems to fit together. This has resulted in my publishing 300 papers andbooks, which some might honor with the title of scientific research.
But curiosity, a keen eye, a good memory and enjoyment of the animal and plant world do notmake a scientist; one of the outstanding and essential qualities required is self-discipline, a quality Ilack. A scientist can be made. A naturalist is born. If you can combine the two, you get the best ofborn worlds.
According to the author, a bern naturalist should first of all be_________ A．full of enthusiasm
B．self-disciplined
C．full of ambition
D．knowledgeable
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