(all examples are taken from BNC)
Could you explain:
when usage and use should be used with (indefinite) article? (as in (2) and (3)),
more clearly - the difference between use and usage when they are used without article, (1),
(I also wanted to ask about the difference between use of and using (when the latter/gerund is used as a noun) - but have understood it while writing a question 3) about (4) :)).