Final answer:
The underlined phrases in the given sentences function as adverb clause, noun clause (direct object), and elliptical clause.
Step-by-step explanation:
- The underlined phrase 'whoever travels on the river' functions as an adverb clause, modifying the verb 'must be'. It provides information about the condition under which one must be brave.
- The underlined phrase 'that they could find gold' functions as a noun clause (direct object). It is the object of the verb 'believed' and answers the question 'what did the miners believe?'.
- The underlined phrase 'whoever found gold' functions as an elliptical clause. It provides a subject for the verb 'caused' and the full form of the clause would be 'whoever found gold caused a frenzy'.
Learn more about Functions of underlined phrases in specific sentences