According to objectivism, man exists FOR HIS OWN SAKE.
Objectivism is a type of philosophical outlook in life. The concept was developed by Ayn Rand, a writer. She expressed this outlook on life in her books. One of the central teaching of Objectivism is that the most important thing in life is to pursue one's happiness. Other teaching of objectivism include the following: reality exist independently of consciousness, direct contact with reality is made through sense perception, etc.
There are two kinds of prepositional phrases: adjective phrases and adverb phrases.
An adjective phrase modifies a noun or pronoun. It always comes immediately after the noun or pronoun it modifies:
Joe is the student with the highest grade. ("with the highest grade" modifies "student.")
An adverb phrase modifies a verb, adjective, or adverb. It is used to tell when, where, how, or to what extent about the word it modifies:
Megan put her bird in its cage. ("in its cage" modifies the verb "put.")
I believe the answer to this is primary source