Error spotting (conditionals & perfect aspect): Identify the erroneous segment (A/B/C) — mark D if there is no error — 'Had I / known it earlier / I would contact you. / No error.' Ensure correct third-conditional form after inversion 'Had I…'

Given data

• (A) Had I
• (B) known it earlier
• (C) I would contact you.
• (D) No error.

Concept/Approach: Third conditional
The inverted form 'Had I + past participle' = 'If I had + past participle'. The result clause needs the perfect conditional: 'would have + past participle'.

Step-by-step correction
1) Keep inversion: 'Had I known it earlier…'2) Change result: 'I would contact you' → 'I would have contacted you.'Correct: 'Had I known it earlier, I would have contacted you.'

Verification
Pattern: If I had known…, I would have called.

Common pitfalls
Using simple 'would' instead of 'would have' in past-unreal results.

Final Answer
C — Use 'would have contacted' after 'Had I known…'