题目内容：
请在第__(50)__处填上正确答案。
A．There have been many attempts to redesign the periodic table since Dmitri Mendeleev drew it up in 1871. B．Railsback has still ordered the elements according to the number of protons they have.
C．"1 imagine this would be good for undergraduates. "
D．Railsback has listed some elements more than once.
E．And the size of element's symbol reflects how much of it is found in the Earth's crust.
F．The traditional periodic table was well drawn.
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