Answer:
Option (A)
Explanation:
In the above-given question,
Option (B) is wrong with it's usage of the modifier "how'' in the sentence. If the modifier is used in one place (how heat from the inner core flows), it should also be used in the continuing clause (how the formation and periodic reversal).
Options (C) and (D) are wrong in using the word "are" for the whole sentence as there is no need to use this word. The verb form will depend on the subject, in this case, is "the discovery that earth's inner core" which is singular in nature. Thus, the verb form will be -is and not -are.
Option (E) is wrong for it's use of the comma. If the comma is used, then the whole sentence is not a full-fledged sentence but rather a dependent clause with no resolution.
The correct answer for the given passage is option (A).
By breaking into a free nation
The other answer is incorrect. The correct answer is stationary.
