Step 1: Understand the word.
The word spasmodic refers to something that occurs at irregular intervals, not continuous or steady.
Step 2: Analyze the options.
Continuous means without interruption, which is opposite.
Gradual means happening slowly over time, not matching the meaning.
Intermittent means occurring at intervals, stopping and starting again, which matches perfectly.
Spontaneous means happening suddenly without planning, which is different.
Step 3: Conclusion.
Thus, the correct answer is Intermittent.