Directions: Fill in the blank by choosing the right form of the given four alternatives.

You will succeed, if you ________ hard.

This is a first conditional sentence expressing a real possibility. When the if-clause uses present tense (or any form implying a real condition), the result clause uses 'will'. Here, 'You will succeed' is the result, so the if-clause should use present simple 'work' (not 'worked' or 'had worked'). First conditionals follow the pattern: If + present simple, ... will + base verb.