Sentence improvement (verb pattern “fail to + base verb”): choose the correct word to complete the infinitive construction Original sentence: "The prosecution failed ___ establish in every case today." Choose the best option that makes the sentence grammatical and natural.

Given data

• Target clause: “failed ___ establish …”.
• Context: reporting that the prosecution could not prove cases in court today.

Concept/Approach
With the verb fail, the standard pattern is fail to + base verb (infinitive). Therefore we need the particle to before “establish.”

Step-by-step correction
Replace the blank with “to” → “failed to establish …”.

Option analysis
to — forms the infinitive “to establish,” which is required after “failed.” ✅on / as / upon — wrong prepositions/particles for this verb pattern.No correction required — incorrect because the sentence without “to” is ungrammatical.

Common pitfalls

• Using prepositions like on/upon after fail; they do not license a following bare verb.

Final Answer
The correct sentence is: “The prosecution failed to establish in every case today.”