Final answer:
Investment spending includes option b, 'changes in business inventories'. This is part of spending on new capital goods, which also encompasses producer's durable equipment, nonresidential structures, and residential structures.
Step-by-step explanation:
The student is asking which of the given options is included in investment spending. According to the definition of investment expenditure, investment spending includes spending on new capital goods, such as producer's durable equipment and software, nonresidential structures like factories and offices, changes in business inventories, and residential structures like homes and apartments. Therefore, option b, 'changes in business inventories', is the correct answer to the question regarding what investment spending includes.