Mother are naturally countable nouns, since we can, clearly, count mothers
D. A source that's cited in another source
Something that is direct means that you get one from place to another the fastest way and without anyone or anything interfering. Indirect means the opposite. It is not the fastest way between two points, and there may be interference or a middleman. An indirect source is one in which the information is not directly from the author of the source, but rather the source using a different source for the information.
