Q1: Which one of the following mistakes/errors may be cumulative + or - :

ANS:C - erroneous length of chain

And you don't see guys at last after or - sign so given answer is correct because erroneous chain gives both error + or - depending on decrease in length or increase in length A and D are cumulative positive errors.
B and C are compensating errors. Errors in bad ranging and sag is always addictive and bad straightening is always subtractive.