Which of the following sentences contains a spelling error?
a. alejandro has always dreamed of building his own sailboat and sailing by himself to the caribbean.
b. angelina wants to use her money to others rather than to acumulate material things for herself.
c. davis and cooper are challenging themselves to run a 5k race, and they are training every afternoon.
d. the decision to put a six-foot tall security fence around the school proved to be very controversial.