Question

select the passage that has a graver tone.

over the low grounds, a thin film of mist was stealing like smoke, marking the distances with a transparent veil. here and there we could see the river faintly flashing in the moonlight.

the gloom that weighed down our hearts was like the fog that stretched along the potomac and enfolded the valley of the shenandoah. a drizzling rain had set in at twilight and, growing bolder with the darkness, was beating a dismal tattoo on the tent.

adapted from j. sheridan lefanu, carmilla and thomas bailey aldrich, quite so

Explanation:

Grave tone conveys sadness, heaviness, or gloom. The second passage uses words like "gloom that weighed down our hearts", "dismal tattoo", and describes oppressive rain/fog, which carry a somber, heavy mood. The first passage has a calm, neutral, slightly ethereal tone about mist and moonlight.

Answer:

The gloom that weighed down our hearts was like the fog that stretched along the Potomac and enfolded the valley of the Shenandoah. A drizzling rain had set in at twilight and, growing bolder with the darkness, was beating a dismal tattoo on the tent.