Read the passage and answer the question. Scientists agree that the earth’s rising temperatures are fuelling longer and hotter heat waves, more frequent droughts, heavier rainfall and more powerful hurricanes. In 2015, for example, scientists concluded that a lengthy drought in California—the state’s worst water shortage in 1,200 years—had been intensified by 15 to 20% by global warming. They also said the odds of similar droughts happening in the future had roughly doubled over the past century. And in 2016, the National Academies of Sciences, Engineering and Medicine announced that we can now confidently attribute some extreme weather events, such as heat waves, droughts and heavy precipitation, directly to climate change. The earth’s ocean temperatures are getting warmer, too—which means that tropical storms can pick up more energy. In other words, global warming has the ability to turn a Category 3 storm into a more dangerous Category 4 storm. Select the most appropriate antonym of the word 'frequent' as used in the passage.

1. Nonstop
2. Irregular
3. Odd
4. Original