The correct option is:

B. Not until we crossed the hill did we see a hug splendid flower bed at the foot of it.

Explanation:
- Option A is incorrect because "No sooner had we crossed the hill when" should be "No sooner had we crossed the hill than."
- Option C is incorrect because "Scarcely had we crossed the hill than" should be "Scarcely had we crossed the hill when."
- Option D is incorrect because "did we saw" should be "did we see."

Option B correctly uses the structure "Not until... did we see," which is grammatically correct and conveys the intended meaning.