在“打网球”这个短语中，“网球”是动词“打”的宾语。

"Tennis" is the object of the verb "play" in the phrase "play tennis".

youdao

I am是动词to be现在时的第一人称单数。

'I am' is the first person singular of the present tense of the verb 'to be'.

《牛津词典》

I have eaten是动词eat的现在完成时；I had eaten是过去完成时；I will have eaten是将来完成时。

'I have eaten' is the present perfect tense of the verb 'to eat', 'I had eaten' is the past perfect and 'I will have eaten' is the future perfect.

《牛津词典》

There's no language in the world that has a rule that says the fifth word has to be a verb.

世界上并没有语言规定,说第五个词必须是动词

耶鲁公开课 - 心理学导论课程节选

Also, current singular versus plural with nouns and verbs.

然后是名词和一般现在时动词的单复数。

韩国人经常犯的失误 - SpeakingMax英语口语达人

So, at the top of 155, he's asked his question. "'Speak,' he commanded. She whispered, 'Love.'" Now, the problem with that is that answer; it's a verb and a noun.

在第155页上部，他问了自己的问题，说吧’,他命令道，她哭着说，爱，现在，问题是这个答案，爱，可以是动词也可以是名词。

耶鲁公开课 - 1945年后的美国小说课程节选