A carpenter makes bookshelves. He is studying how much money he can earn in one year. Choose the three variables that are most important for him to study.
A. the weight of each bookshelf
B. the cost of building a bookshelf
C. the dimensions of each bookshelf
D. the time it takes to build each bookshelf
E, the price customers will pay for a bookshelf
J
F. the number of different designs he can build