Which of the following is an example of investment in human capital?
A. A carpenter invests in a training course and learns how to make cabinets and drawers faster
B. A photographer invests in new software that allows him to edit his pictures faster and service more clients
C. A firm invests in a new 3D printer that makes parts three times faster than the old method
D. A factory invests in a new procedure using the same equipment that allows it to create more products