Adrawback to an installment plan is that
a. it takes longer to buy a product
b. a large down payment is required.
c. interest rates are generally very high
d. interest rates are generally very low

The correct answer should be C.interest rates are generally very high
They are recalculated all the time and on a yearly basis and sometimes for high mortgages you end up paying back as much as double of what you took initially. You get the product instantly but you pay a lot more than what it's worth in the long run so one generally should try to avoid them.