(1) I think that the answers may be:
(a) I suggested that my friend play (subjunctive).
(i) The teacher suggests that Mona study more.
(b) To hear my friend say that was unusual. The full sentence
is To hear my friend to say [infinitive] that was unusual.
(i) English speakers have decided that after certain verbs such as
hear, they drop the to.
Student or Learner