In Paragraph 4, the pronoun "it" refers to ______.

A．To call on the readers to protect homing pigeons from extinction.
B．To offer the reader information about homings pigeons and their training.
C．To appeal to the owners of homing pigeons to set the birds free.
D．To convince the reader it worthwhile to keep a homing pigeon as pet.

A．unlike big seed companies, Seed Savers Exchange do not sell seeds to people
B．Seed Savers want to prevent large-scale spreading of disease among plants by breeding new types of plants
C．growing limited types of plants may endanger our food supply, because large scale spreading of disease is more likely to occur
D．big seeds companies try to protect food supply by breeding hybrid plants