18. = 4. infinitive phrase: to + verb is an infinitive
19. = 3. gerund phrase: -ing form of a verb can either be a present participle or a gerund, but if it functions as a noun in a sentence, then it is only a gerund
20. = 5. independent clause: a clause that can exist on its own
21. = 2. participial phrase: these phrases are often used as adjectives
22. 1. prepositional phrase: according to is a preposition, and any combination of words which doesn't have a finite verb in it is a phrase
23. = 6. noun clause: functions as a noun (in this case, a direct object), but has a finite verb, as any clause does
24. = 7. adjective clause: it describes the noun before it. What kind of tools? (those) by which...
I am not sure about the last one though, because I cannot see what is italicized in the final sentence. If only than great riches is italicized, than it has to be a phrase, and the only remaining option is adverb clause, but it is not a clause because there is no verb italicized.