阅读下面短文，从短文后各题所给的四个选项（A、B、C、和D）中，选出可以填入空白处的最佳选项，
After spending a weekend away with my adult son, I was so impressed by his generous heart that I sent him this letter.
Dear son,
I want to thank you for teaching me a very 36 lesson in life by the great example you 37 . When we were eating at that café in Bondi and a person who had 38 his hamburger didn’t have enough money to pay for it, without any 39 , you went over and put the 40 $2 into his hand.
When we were leaving, you 41 threw a five-cent coin onto the pavement and said 42 like, “Some kid will really enjoy 43 this.”
Last week, a young man 44 me in the line at a petrol station didn’t have 45 money to pay for his petrol. I asked the money collector, “How much 46 is he?” She told me he had meant to put $15 of petrol in his car 47 he had been looking at the wrong gauge(计量表) and had put in 15 48 , which came to just over 49 . That is an easy mistake 50 both gauges run fast.
Something made me think of you and 51 you did that night at the café in Bondi. I handed the man $6. He was so 52 and said, “But why would you do this for me?” I just smiled as I thought of you.
Thank you, son, for teaching me that “it’s 53 to give than receive”. Now when I see a five-cent coin on the 54 and want to pick it up, I think of you and leave it 55 , just in case some kid will get a kick out of finding it.
Love always, Mum
36. A. humorous B. private C. reasonable D. valuable