Step 1: Understand the idiomatic expression.
The correct idiomatic expression is "Look before you leap," which means to consider the consequences before acting. "Look" is the base form of the verb used here. Step 2: Analyze each option.
- (A) Look: Correct. "Look" is the correct verb form to use in this idiomatic phrase.
- (B) To look: Incorrect. "To look" is the infinitive form and is not appropriate here.
- (C) Looking: Incorrect. "Looking" is the present participle and is not used in this expression.
- (D) Looked: Incorrect. "Looked" is the past tense and does not fit in this context. Step 3: Conclusion.
The correct sentence is "Look before you leap."