In the following sentence, a blank is given. Choose the most appropriate word to complete the sentence meaningfully: Only when _____ failed, the army resorted to force.

Introduction / Context:
This is a vocabulary based sentence completion question that checks a learner's ability to select the most suitable word from a set of options so that the sentence makes logical and idiomatic sense. The sentence talks about the army using force only after some other approach had failed. This type of question requires attention not only to dictionary meaning but also to typical combinations of words and real life logic.

Given Data / Assumptions:
- Sentence: Only when _____ failed, the army resorted to force.
- Options: efforts, arrests, persuasions, manipulations.
- The blank refers to something that can fail before an army decides to use force.
- The context implies that some peaceful or non violent means was tried first.

Concept / Approach:
In real situations, an army or authority usually tries negotiation, persuasion or diplomatic efforts before resorting to force. The phrase Only when blank failed, the army resorted to force suggests that some method other than force was attempted earlier. Among the given options, persuasions fits this idea best, because persuasion refers to attempts to convince others by argument or appeal. Efforts is possible but less precise, arrests and manipulations do not match the typical logical sequence that would justify later use of force.

Step-by-Step Solution:
Step 1: Interpret the basic meaning of the sentence. It claims that force was used only after another approach had not worked.Step 2: Check each option. Efforts is a general word that can refer to any kind of attempt, but it does not highlight peaceful negotiation.Step 3: Arrests means taking people into custody, which is already a form of coercion rather than a step before force.Step 4: Persuasions refers to attempts to convince people through reasoning or appeals and is therefore a clear non violent method that can be tried before force.Step 5: Manipulations suggest secret or unfair control, which does not suit a neutral examination sentence about an army.Step 6: Thus, persuasions is the best fit. The complete sentence becomes: Only when persuasions failed, the army resorted to force.

Verification / Alternative check:
We can test the sentence with each option. Only when efforts failed, the army resorted to force is grammatical but vague. Only when arrests failed sounds illogical because arrests are already strong actions. Only when manipulations failed gives a negative impression that the army was behaving in an unethical way, which is unlikely for a neutral exam sentence. Only when persuasions failed, the army resorted to force reads natural and matches the usual progression from soft measures to strong measures.

Why Other Options Are Wrong:
- Efforts is too general and does not clearly indicate a contrast with force, although not strictly wrong, it is not the best choice among the given words.
- Arrests represent a severe legal or forceful step, not something tried before the use of force by soldiers.
- Manipulations implies underhand control and does not fit a formal context that aims to be neutral and balanced.

Common Pitfalls:
Candidates sometimes choose a word simply because it seems grammatically correct, without checking if it matches the context. Another common error is ignoring the logical sequence in the real world, for example choosing arrests without recognising that this is already a harsh measure. To avoid such mistakes, always imagine the situation described by the sentence and ask which option naturally fits that scenario. Words related to diplomacy and negotiation usually appear before any reference to force or violence.

Final Answer:
The correct word to complete the sentence is persuasions.