Read the sentences from the sections "The Atoms" and "The Electrons."
There is a separate box of elements below the main table (and an odd shape for the main table, with a bite taken out of the top) because of how the other parts of the atom – the electrons – are arranged.
In other words, the first element in each row starts a new shell containing one electron, and the last element in each row has two of the subshells in the outer shell fully occupied.
The two sentences develop the reader's understanding of the article by ____.
A
describing an effect on the design of the periodic table and its cause
B
explaining a problem with the design of the periodic table and its solution
C
illustrating how the design of the periodic table has changed over time
D
creating a sequence of steps for reading the design of the periodic table