Which of the following statements about redemption of a mortgage upon the death of a breadwinner is correct?

$($Search Chapter $3)$

a$.$ It is never appropriate to pay off a mortgage on a principal residence.

b$.$ A mortgage should always be paid off upon the death of a breadwinner.

c$.$ A house mortgage is always payable in full upon a breadwinner's death.

d$.$ Survivors having the option to pay off an existing home mortgage at a breadwinner's death usually means having sufficient funds to redeem the mortgage.