This could have worked if I ----been more cautious.
A
had
B
have
C
might
D
would
Correct Answer: had
3rd conditionl - এর নিয়মানুসারে Principal Clause - এ could have / would have /might have থাকলে if clause টি Past Perfect হবে। সুতরাং শূন্যস্থানে Past Perfect - এর auxiliary verb 'had' হবে।