The correct answer is E. judicious.
A judicious selection is a careful and thoughtful choice. When one cannot read every book, it is important to make a selection of books that are well-written, informative, and relevant to one’s interests. A judicious selection will help one to get the most out of the time that one has to read.
The other options are not as appropriate in this context. A normal selection would be a typical or average selection. A standard selection would be a selection that meets a certain level of quality. A sample selection would be a small selection that is representative of a larger group. A moderate selection would be a selection that is not too large or too small.
It is important to make a judicious selection of books because reading is a valuable activity that can help one to learn and grow. By making a careful choice of books, one can ensure that one is getting the most out of the time that one has to read.