根据下列内容，回答216-220题。
Looking back on my childhood，I am convinced that naturalists are born and not made．
Although We were brought up in the same way，my brothers and sisters soon abandoned their pressed flowers and insects．Unlike them，I had no ear for music and languages．1 was not an early reader and I could not do mental arithmetic.
Before World War I we spent our summer holidays in Hungary. I have only the dim memory of the house 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, the farm 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 enthusiasm has led me into varied investigations. I love discussing my favorite topics and enjoy burning the midnight oil, reading about other people's observations and discoveries. Then something happens that brings these observations together in my conscious mind. Suddenly you fancy you see the answer to the fiddle, because it all seems to fit together. This has resulted in my publishing 300papers and books, 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 not make a scientist; one of the outstanding and essential qualities required is self-discipline, a quality I lack. A scientist can be made. A naturalist is born. If you can combine the two, you get the best of both worlds.
According to the author, a born naturalist should first of all be__________.

A.full of ambition
B.self-disciplined
C.full of enthusiasm
D.knowledgeable