Choose the correct option from the following.

Work hard lest you ______ fail.

should

The correct answer is Option (4) - should

• The phrase "lest you should fail" is a formal construction used to express a precaution or warning to avoid something undesirable.
• "Should" in this context refers to a possibility or hypothetical situation.
• The other options ("will," "could," and "should not") are not grammatically correct in this structure.