不好意思，想請問大家這篇。
第二段:
When the German chemist Lothar Meyer and (independently) the Russian Dmitry
Mendeleyev first introduced the periodic table in 1869-70, one-third of the
naturally occurring chemical elements had not yet been discovered. Yet both
chemists were sufficiently farsighted to leave gaps where their analyses of
periodic physical and chemical properties indicated that new elements should
be located. Mendeleyev was bolder than Meyer and even assumed that if a
measured atomic mass put an element in the wrong place in the table, the
atomic mass was wrong. In some cases this was true. Indium, for example, had
previously been assigned an atomic mass between those of arsenic and
selenium. Because there is no space in the periodic table between these two
elements, Mendeleyev suggested that the atomic mass of indium be changed to a
completely different value, where it would fill an empty space between
cadmium and tin. In fact, subsequent work has shown that in a periodic table,
elements should not be ordered strictly by atomic mass. For example,
tellurium comes before iodine in the periodic table, even though its atomic
mass is slightly greater. Such anomalies are due to the relative abundance of
the "isotopes" or varieties of each element. All the isotopes of a given
element have the same number of protons, but differ in their number of
neutrons, and hence in their atomic mass. The isotopes of a given element
have the same chemical properties but slightly different physical properties.
We now know that atomic number (the number of protons in the nucleus), not
atomic mass number (the number of protons and neutrons), determines chemical
behavior.
6. It can be inferred from paragraph 2 that tellurium comes before iodine in
the periodic table even though tellurium's atomic mass is slightly greater
because
○iodine is less common than tellurium
○both iodine and tellurium have no isotopes
○the chemical behavior of tellurium is highly variable
○the atomic number of tellurium is smaller than that of iodine
答案是D， 可是要從哪推論出來，我左看右看都看不出端倪= =
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