Regarding 3;
The previous poster is correct, 'small' amounts of frost in the vicinity of the fuel tanks are allowed BUT the question doesn't say that so I'd be cautious and say A.
Thank you very for your help.
In the question regarding frost on wings, answer A says "all deposits of frost must be removed from the wings before flight", so i assume that it means that even small ammounts must be removed and are not acceptable in any way.
Now, it is said in my book that many aircraft maintenance book allow thin layers of frost to build up over the lower part of the wings, but it's not necessarily approved by the CAA or any other administration : it depends on the manufatcurer.
That's why i definitely don't know what's the right answer.
What do you think about this?