The face of the water, in time, became a wonderful book — a book that was a dead language to the uneducated passenger, but which told its mind to me without reserve, delivering its most cherished secrets as clearly as if it uttered them with a voice. And it was not a book to be read once and thrown aside, for it had a new story to tell every day. —Life on the Mississippi,
Mark Twain

What main idea does this passage convey about the river?
A - The river is meaningless to most people
B - The river is wonderfully different each day
C - The river protects its secrets
D - It is easy to get to know the river