Identify the part of the sentence that contains an error.
If I had known / this before, / I will have helped him.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → I will have helped him
This sentence talks about a past that did not happen. The speaker did not know, so he did not help. For such a past condition the if-part takes the past perfect: had + past participle (V3). The main part takes would have + V3. The clue is “had known”. So “will have helped” should be “would have helped”.
Option 1: If I had known — No error. The past perfect “had known” is right in the if-part of a past condition that did not happen.
Option 2: this before, — No error.
Option 3: I will have helped him — Error. “will have helped” should be “would have helped”.
Corrected: If I had known this before, I would have helped him.