-- Why do you look sad?

-- There are so many problems _____.

A. remaining to settle                   B. remained settling

C. remaining to be settled             D. remained to be settled

---Why do you look sad?

   ---There are so many problems______.

   A. remaining to settle                                 B. remained settling  

C. remaining to be settled                           D. remained to be settled

--- Why do you look sad?

---There are so many problems ______.