How Does the Textbook Define the "Hidden Curriculum

How does the textbook define the "hidden curriculum"?

A) the ideal of a self-denying, highly moral life accompanied by self-sacrifice
B) higher grades given for the same work, or a general rise in student grades without a corresponding rise in learning
C) subjects that are rarely taught, which require students to seek them out on their own time
D) lessons that students learn indirectly through the method in which the curriculum is presented and the way the school is organized