Answer:
Participle: "reminding"
Modified: guide
Explanation:
A participle is a word that has verb characteristics and can also function as both a verb and an adjective. They are also used to modify the words in a sentence.
In the given sentence "[R]eminding the younger children to walk carefully, the guide led the group into the cave", the participle is "reminding", taking the "-ing" form of the verb. And the word it modifies is "the guide".
Thus, the correct answer is
Participle: "reminding"
Modified: guide
