Final answer:
In the sentence given, a colon should be inserted after the word 'tenses' to introduce the list of the six verb tenses mentioned.
Step-by-step explanation:
The question asks to identify where a colon should be inserted in the sentence: "Verbs have six tenses past, present, future, past perfect, present perfect, future perfect". A colon is used before a list or an explanation that is preceded by a clause that can stand by itself. Thus, the appropriate place to insert the colon is after the word 'tenses', because what follows is a list of the six tenses.