Answer:
a story is about to Begin
"once upon a time" is an example of the use of sequence words
Explanation:
When we hear the phrase "once upon a time" we know that a story is about to Begin. and This phrase is an example of a sequence of words .
Sequence words are used to mainly organize a story so that the reader can understand the events that occurred in the story . examples of such words include : "then" , "when" "later" and so on
