59. Electromagnetic traps for atomic ions work well for experiments using a small number of ions __ they are completely impractical for large-scale systems. A. so long as B. now that C. although D. in case E. whether

## Step 1<br />The sentence is discussing the limitations of electromagnetic traps for atomic ions. It states that these traps work well for experiments using a small number of ions, but they are completely impractical for large-scale systems. The conjunction that needs to be inserted should express this contrast between the two situations.<br /><br />## Step 2<br />Let's analyze each option:<br />- A. "so long as" implies a condition, which doesn't fit the context of the sentence.<br />- B. "now that" implies a point in time, which is not relevant here.<br />- C. "although" introduces a contrast, which fits the context of the sentence.<br />- D. "in case" implies a precaution or a hypothetical situation, which is not relevant here.<br />- E. "whether" is used to introduce alternatives, which is not relevant here.<br /><br />## Step 3<br />Based on the analysis, the correct answer is C. "although". It introduces the contrast between the two situations: electromagnetic traps working well for small-scale systems and being impractical for large-scale systems.