Incidentally there are techniques that should be understood for exams with multiple choice answers.
Usually there is not a penalty for getting an answer wrong. That means if you do not know the answer it is always worth guessing - there is a chance of randomly selecting the correct answer.
If you can weed out some of the answers as being definitely incorrect, but can't choose betwen the others, then just guess between the others - again you have a chance of getting it right.
One way of guessing is to pick answer c). Studies of exams (in all subjects) show that this is the preferred place for the correct answer. Examiners seem to be too lazy to properly randomise.
In the set of answers offered in the OP's case I'd definitely pick c) - it also has a more precise value than the others so its tempting to think that's the right one. But it could be a double bluff by the examiner, deliberately to tempt you to pick the wrong answer... (this way madness lies)
H