Sentence Correction

Since children who undergo preshool education have (been proven to be less liable)
to need remedial programs later, preschool education programs are demonstrably cost effective.

a. been proven to be less liable
b. proved themselves not as liable
c. proved to be less likely
d.proven to be less liable
e. proven themselves not as likely

oa C

Likely is better so left with C and E..
Going with c

Isnt it necessary to use proven with have instead of proved?

Third degree of prove?

Please help.

Thanks.

why is proven and liable wrong!!??