Question

read the dictionary entry.
foolproof (adj): 1 designed to function despite human error 2 without possibility of failure
which sentence uses the word foolproof as described by the second definition?
the new computers were not foolproof in the hands of untrained users.
scientists were certain that despite being out of their control, the space probe would be foolproof.
the defense lawyer concluded his remarks with a foolproof argument of the defendant’s innocence.

Explanation:

The second definition of "foolproof" is "without possibility of failure".

1. The first sentence states the computers were not foolproof for untrained users, which refers to failing due to human error (matches definition 1, not 2).
2. The second sentence says the space probe would be foolproof despite being out of control, meaning it cannot fail regardless of external circumstances (matches definition 2).
3. The third sentence's "foolproof argument" means it works despite attempts to challenge it (aligns more with definition 1, as it resists human counteraction/error, not that it has no possibility of failure entirely).

Answer:

Scientists were certain that despite being out of their control, the space probe would be foolproof.