阅读下面短文，从各题所给的A、B、C、D四个选项中，选出填入空白处的最佳选项。
Whenever the sun dropped and the blue sky came up, my
father and I used to climb the mountain near my house. 1 together, my
father and I used to have a lot of conversations through which I 2 lessons from
his experiences. He always told me, "You should have goals like climbing the
mountain." Without the mountains-climbing 3 we both enjoyed,
we couldn't have enough time 4 together because
my father was very busy. I 5 got a lot from
mountain-climbing.
Once we
climbed a very 6 mountain. It
was so challenging for me 7 I was only ten
years old. During 8 first few hours
of climbing, I enjoyed the flowers and trees, and the birds' singing, but as time
9, I got a pain in both of my legs, I wanted to give
up 10. In fact, I hated it at the moment, but my father said
to me, "You can always see a beautiful sky at the top of the 11, but you can't see it 12 you reach the top. Only there at the
top, can you see all of the nice things, just like 13 life."
At that time, I was too young to understand his
words. But 14 after that, I
get new hope and confidence. I found 15 standing at the
top of the sky, which was as clear as crystal(水晶)
