Research and development costs:A. should be included in the cost of the patent they relate to. B. are capitalized and then amortized over a period not to exceed 20 years. C. are incurred as expenses only when R&D is successful. D. must be expensed when incurred under generally accepted accounting principles.

D) must be expensed when incurred under generally accepted accounting principles.

Explanation:

Research and development costs are costs associated with developing new products or the discovery of new knowledge about scientific and technological goods and services.

Before 1974, R&D costs were capitalized as intangible assets, but then in 1974 the Financial Accounting Standards Board (FASB) ruled that companies must expense all R&D costs when incurred.