Fill in the blank with the most appropriate word from the options giv…

The correct answer is Option (1) → most promising

Superlative of a long adjective:

• Short adjectives take -est (tall → tallest); longer adjectives take most before them (promising → most promising).
• "Most" is never added to a form that is already superlative (best, tallest).
• This sentence: the council chose the best of several proposals, the one with the greatest chance of success, so the superlative most promising is needed.
• Complete sentence: The council zeroed in on the most promising proposal after hours of serious deliberations.
  Example: This is the most promising plan we have received so far.

Why the Other Options are Incorrect?

Option 2: promised — Incorrect. Promised is a past participle; "the promised proposal" would mean a proposal that someone had promised, not the best one chosen.

Option 3: promise — Incorrect. Promise is a noun or a verb; "the promise proposal" is not English, as the blank needs an adjective.

Option 4: most best — Incorrect. It is a double superlative: best is already the superlative of good, so "most" cannot be added.