For what reasons might discounted cash flow valuation be difficult for the following types of firms in the situations stated?

A. A private firm, where the owner is planning to sell the firm.

B. A biotechnology firm with no current products or sales, but with several promising product patents in the pipeline.

C. A firm in the process of restructuring, where it is selling some of its assets and changing its financial mix.

D. A firm which owns a lot of valuable real estate that is currently not utilized.