Q
Medium 1 Mark
English Conditional Sentences
Choose the correct sentence.
Explanation
Since both the cause and the result are firmly in the finished past, the sentence needs the full third conditional pattern: "had been backed up" with "wouldn't have lost," not a mixed or shifted tense.
Reference: Skoolyst English Grammar Guide , Page 8
Hint
If both the cause and the consequence happened entirely in the past, don't shift either clause into the present.