Correct Option (B)
The passage states that a military takeover is likely in developing countries when political leadership "fails to emerge." This directly implies that the military steps in to occupy a void created by the absence or inadequacy of civilian political authority. The core assumption is that the military intervenes to fill a political vacuum that arises from the failure of established political leadership.
Incorrect Options:
(A) political leadership is not an effective instrument. The passage focuses on the failure to emerge of political leadership, rather than asserting that political leadership is inherently ineffective as an instrument. The problem highlighted is the absence or breakdown of leadership, not its general lack of efficacy.
(C) military intervention is inevitable for development. The passage indicates that military intervention and withdrawal are "closely related to a society’s level of political development." This suggests a correlation or influence, implying that the level of political development affects military involvement. It does not state that military intervention is a necessary or inevitable precursor for a country's development. In fact, a higher level of political development would typically be associated with a reduced likelihood of military intervention.