If it is a MCQ, I would choose D. as my interpretation of "random selection procedure" is to ensure that each respondent has the same chance of being selected into the sample.

in D, the goal is to have a sample test whether the products are produced according to the expected value.

A = to me is an intended selection
B = to me is the making of observation so as to make a conclusion on the frequency of letters used in the book.
C = to me the purpose of the selection is not clear