An infinitive is the basic form of a verb. So the most likely answer is C. I am sorry if this is incorrect but I'm not sure
Zaroff is weeding out the weak and degenerates to better fill the gene pool with stronger people rather than weaker ones
The subject of a media piece could affect: all of the above (when it is broadcast; whether is effectively received; who reads it; what the producer intends for it to do for a viewer).