Answer
(a) phosphoric acid
(b) sulfurous acid
(c) hydrotelluric acid
Work Step by Step
(a) phosphoric acid
If the oxoanion ends in $-ate$, then we drop this ending, substitute the ending $-ic$ in its place, and add the word $acid$ to the end.
(b) sulfurous acid
If the oxoanion ends in $-ite$, then we drop this ending, substitute the ending $-ous$ in its place, and add the word $acid$ to the end.
(c) hydrotelluric acid
If the name of the anion ends in $-ide$, then we add the prefix $hydro-$ to the anion, change the anion ending from $-ide$ to $-ic$, and add the word $acid$ to the end.