Insert the correct Adverbial Phrase in the blank space: Only ______ is there a rumble in the sky.

Correct answer: occasionally

Explanation: We need an adverbial phrase of frequency that makes sense with rumble in the sky (which usually refers to thunder). A. occasionally ✅ – correct, because thunder does not occur all the time, only sometimes. B. swiftly ❌ – shows speed, not frequency. C. quite ❌ – intensifier, doesn’t fit the structure. D. merrily ❌ – means happily; makes no sense with rumble in the sky. ✔ The meaningful completion is: “Only occasionally is there a rumble in the sky.”