Hi
aladdin, this question relates to turning errors on direct reading compasses. These occur not because the aircraft is turning but because it is banking, and on certain headings the compass card is allowed, because of the bank, to line up or to attempt to line up with the lines of magnetic flux which are not level with the earth's surface but dive into it at an angle of dip in excess of 60 deg at 50N. The swirl of the liquid in the compass can add to or reduce this effect. There is a good explanation
here , page 7.24 on, titled 'dip errors'. I use the acronym UNOS for the northern hemisphere, meaning
Undershoot on turns to
North and
Overshoot on turns through
South
The amount to undershoot or overshoot the target heading on turns clearly depends on bank angle, dip (ie magnetic latitude) and target heading. There are various rules of thumb to allow you to estimate this. The FAA Instrument Flying handbook
here contains a rather spurious explanation for turning error on page 5.12 together with some rules of thumb for this undershoot or overshoot. On page 7.22 there are some entirely different rules of thumb. In my limited experience these are both of questionable accuracy, and the example in the second case only seems to work because they choose a latitude of about 30N.
When the JAA exams started the UK CAA were asked which rules of thumb we should follow for the exams and they said 'always undershoot or overshoot by 20 to 30 degrees, irrespective of bank angle, and in the exam turns will be on to north or south'. Consequently we apply this rule for the exam, and therefore the answers to your questions should be (a) and (c).