[theseoafs]

A is indented with a tab.

B is indented with a tab, plus the requisite number of spaces to line up with the above line.

C is indented with a tab.

[abecedarius]

Does anyone actually do that? I've never noticed that style in any code I've read, but maybe that just means it works.

[theseoafs]

I don't think anyone manually counts out their tabs and spaces, but I think every major text editor has a mode or plugin to make this automatic.