1、Unfrequent sightings of this rare bird have made it a popular subject among birdwatchers.
很少见到这种稀有的鸟，使它成为鸟类观察者中的热门话题。
2、Because of its unfrequent use, the word "unfrequent" may be unfamiliar to many people.
由于很少使用，"unfrequent" 这个词可能对很多人来说并不常见。