Fill in the blank with the most appropriate preposition:

We can make no progress if we continue working _____ these conditions.

under

The correct answer is Option (2) → under

The preposition under is used to indicate a state, situation, or condition by which an action is governed or limited. To work under conditions means to operate while being subjected to or constrained by those particular circumstances.

The sentence implies that the current conditions are unfavorable and preventing progress, making under the correct choice.