Explanation:
correct is (if only one answer is correct) :
he will take longer, if he checks all the books instead of checking a few.
if 2 answers are correct, then
he will not need a list of all the books
is also correct.
the tricky part here is to understand what is meant by "list".
if it means a printed paper list in addition to all the books on shelves, then this is not needed, as he can go and pick books from the shelves without knowing which ones are there or even how many are there in total.
but if the books on the shelves are the "list" itself, then this is needed, of course.
the option
he will have a more representative sample, if he chooses randomly
is not true.
there is nothing more representative than checking every item, one after the other. and picking fully randomly has a big risk of missing whole subgroups with special "behavior".
in the same way also picking only the books he likes has a big risk of missing large subgroups with different behavior.
and this is therefore not true either.