单项选择题
Summers with father were always enjoyable. Swimming, hiking, boating, fishing—the days were not long enough to contain all of our activities. There never seemed to be enough time to go to church, which disturbed (扰乱，使不安) some friends and relations. Accused (谴责) of neglecting this part of our education, my father instituted (制定，开始) a summer school for my brother and me. However, his summer course included ancient history, which Papa felt our schools neglected, and navigation (航海), in which we first had a formal examination in the dining room, part of which consisted of tying several knots in a given time limit. Then we were each separately sent on what was grandly referred to as a cruise (巡航) in my father’s 18-foot knockabout, spending the night on board, and loaded down, according to my father, with enough food for a week. I remember that on my cruise I was required to formally plot our course, using the tide table, even though our goal was an island I could see quite clearly across the water in the distance.
Why did the author have to plot the course of his cruise（） A. He had to demonstrate his ability to do so.
B. The coast was dangerous.
C. He was afraid of getting lost.
D. The tides were strong.