Who is Calling?

is.na() is a primitive generic. In the console, look at its available methods.

When you call is.na(list(TRUE, FALSE, NA)), which of the following statements is true?

50 XP

data.frames are lists, so is.na.data.frame() is called.
Neither is.na.list() nor is.na.default() exist, so an error will be thrown.
Since neither is.na.list() nor is.na.default() exist, the primitive is.na() is called.
lists are rasters, so is.na.raster() is called.