How could a user substitute all instances of C with omputer in a file named nstructions and display the results in the terminal window?

How could a user substitute all instances of C with omputer in a file named nstructions and display the results in the terminal window?

A.
cat instructions | awk C omputer

B.
cat instructions | awk ‘/PC/ print omputer’

C.
sed s/PC/computer/g instructions

D.
sed -s PC -r computer instructions