What has anna done the would form the foundation of a friendship

to persuade readers which is answer c

the answer can be "credo" it means to believe = the word credo means "an official statement of beliefs"

the pronoun reference replaces a noun, but you have to make sure there's no room for confusion.

in the first sentence "her" could be referring to shely or to the sister. the answer there is "shelly called her sister and told her about the new baby."

in the second sentence "it" could be referring to the roof or the floor. the answer there is "since the roof leaks on the family room floor, we need to repair the roof."

your awnser would be b.