This could have worked if I _______ been more far-sighted.

Main clause এ could/might + have + PP of verb থাকলে, if clause এ had + PP of verb হয়।
তাই, If clause টি হবে I had been more far-sighted.

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Structure of conditional sentence:

• Zero Conditional = If + Present + Present (shows scientific and general truth)
• 1st Conditional = If + Present + Future
• 2nd Conditional = If + Past Simple + Future in Past (S + would/might/could + Base Form of the Verb)
• 3rd Conditional = If + Past Perfect (had +V3) + Perfect Modal (S + would have/could have/might have + V3)

বা clause গুলোকে উল্টে দিয়েও লিখা যায় -
• 1st Conditional = Future + If + Present.
• 2nd Conditional = Future in Past (S + would/might/could + Base Form of the Verb) + If + Past Simple. 
• 3rd Conditional = Perfect Modal (S + would have/could have/might have + V3) + If + Past Perfect (had +V3).

If মাঝে থাকলে কোন কমা বসে না, কিন্তু if প্রথমে থাকলে দুইটি clause কে আলাদা করার জন্য মাঝে কমা বসাতে হয়।