一个（Phenomenon）是单数，另外一个（Phenomena）是复数。

Phenomenon comes to English from Greek through Latin—kind of like criterion, which came directly from Greek.

Phenomenon来源于拉丁语，后从希腊来到英国，这种情况有点像criterion，直接来自希腊。

Singular

Phenomenon 
Criterion

Plural

Phenomena 
Criteria

Quick and Dirty Tip: Remember that phenomenon is singular by noting that the non at the end sounds likeone.

应急提示：可以通过该单词的末尾non有点像one这一点来记住phenomenon是单数。