Whenever the sun dropped and the blue sky came up, my father and I used to climb the mountain near my house. Walking together, my father and I used to have a lot of conversations through which I learned lessons from his experiences. He always told me, "You should have goals like climbing the mountain." Without the mountain-climbing that we both enjoyed, we couldn't have enough time to spend together because my father was very busy. I really got a lot from the mountain-climbing. It gave me time to talk with my father and to be in deep thought as well as develop my patience. Once we climbed a very high mountain. It was so challenging for me because I was only ten years old. During the first few hours of climbing, I enjoyed the flowers and trees, and the birds' singing. But as time passed, I got a pain in both of my legs. I wanted to quit climbing, but my father said to me, At that time, I was too young to understand his words. But later after that, I got to know the meaning of hope in life. I found myself standing at the top of the mountain, and the sky was as clear as . The passage tells us that mountain-climbing was    _    for the father and the son.
hard enjoyable painful comfortable