Re-write the following sentences according to the instructions given after each. Make other changes that may be necessary, but do not change the meaning of each sentence.
Every one of them was an experienced mountaineer. (Begin: There was no ..................)
Topic: Transformation — affirmative to negative
Answer
There was no one among them who was not an experienced mountaineer.
This converts an AFFIRMATIVE into a NEGATIVE with the same meaning, using a DOUBLE NEGATIVE: Affirmative: EVERY ONE of them WAS an experienced mountaineer. Negative: There was NO ONE among them who was NOT an experienced mountaineer. Two negatives — "no one" and "was not" — cancel out and restore the original sense.
THE TRAP is to write "There was no one among them who was an experienced mountaineer", which says the exact opposite. The second negative is essential and is the mark.
The pattern, worth learning because it recurs (the 2018 paper sets the same conversion with a black sheep):
Every X is Y → There is no X who is not Y
After converting, always read your answer back and check it still means what the original meant.