Read the passage:
one cannot easily realize what a tremendous thing it is to know every trivial detail of twelve
hundred miles of river and know it with absolute exactness. if you will take the longest street in
new york and travel up and down it, conning its features patiently until you know every house and
window and lamppost and big and little sign by heart, and know them so accurately that you can
instantly name the one you are abreast of when you are set down at random in that street in the middle of an inky black night, you will then have a tolerable notion of the amount and the
exactness of a pilot's knowledge who carries the mississippi river in his head.

which description develops the experience of learning to navigate the mississippi river.

a) you will then have a tolerable notion of the amount and the exactness of a pilot's
knowledge who carries the mississippi river in his head.

b) when you are set down at random in that street in the middle of an inky black night.

c) one cannot easily realize what a tremendous thing it is to know every trivial detail of twelve hundred miles of river.

d)if you will take the longest street in new york and travel up and down it, conning its
features patiently until you know every house and window and lamppost and big and little sign by heart.