Question

No matter what experience you have had with forest fires, if you would have witnessed the fire roaring down through the canyon, you would have been terrified.

• A. If you witnessed
• B. If you had witnessed
• C. If you could witness
• D. No change

Answer 1

Answer: (B)

If you had witnessed

The sentence indicates a condition that could have happened in the past. There is a 'would have' in the second part of the sentence but it should not be repeated in the first one, because of the use of 'would have' is done as a possibility of an effect of something done in past. So generally would have will be followed by a past perfect verb., that is had+past participle, here, had+witness(ed). Hence, Option A is correct. The rest of the options do not adhere to this rule, hence incorrect.