a. False. This refers to the inherent optical density of the film material plus unexposed developed emulsion. This should be less than 0.2. However, film that has been stored for too long a period or at too high a temperature may have higher values, in which case it should not be used. 

b. False. Film speed is a measure of film sensitivity when exposed, i.e. a high-speed film requires less exposure to produce a certain optical density than a film of low speed.

c. True. Films with narrow latitude require a smaller range of exposures to achieve darkening over the useful optical density range, i.e. they provide good contrast between tissues. Wide-latitude films are the reverse, requiring a greater range of exposures to achieve this range. 

d. True. Film gamma refers to the slope of the linear part of the characteristic curve and is the ratio of the differences between optical density and film exposure at two given points on the slope. If gamma increases, then film latitude decreases and contrast increases. These are inherent properties of any given film. 

e. True. The optical densities for each layer are cumulative so that, for a given exposure, the total optical densities will be greater than using a single layer. This assumes that the total thickness of emulsion is doubled.