What sentence in Acacia by the Window best highlights my love for Yang Huai?

A few years ago, there was a locust tree in front of my office window, which was as high as three or four floors. It must have grown there a long time ago, because I found the tree when I attended the completion acceptance of the office building. At that time, I thought to myself, I must not share the office blocked by the canopy, which is dark and lacks vision.

Unfortunately, I happened to be in that office and was depressed for a long time. I suggested cutting down that eyesore tree, but it didn't come true because it wasn't taken seriously.

In the first spring, the willows were all green and more and more lush, and this acacia tree was bare and gray, with a winter face and a few dead branches sticking up stubbornly. Maybe a psychological enemy. I really don't appreciate its posture. I was glad that it would surely die if it didn't germinate, so I imagined that it might die in two situations: the tree was too old, the roots were aging, or the roots were injured when building an office building and digging the foundation.

One morning, when I opened the window to get some air, I felt a familiar smell of My Sweetie flowing indoors, but I couldn't remember what it was at the moment. Maybe it's perfume sprayed on my female colleague at the same table. When I asked, I shook my head at the table: I've never sprayed that thing. At this time, I looked up and saw the locust tree in front of the window. I almost forgot about this tree. I don't know when it bloomed a bud the size of a soybean, and the branches also appeared a layer of light green. Alas, this acacia tree that has died in my heart has already reported spring to me! This unexpected discovery made me hurry to the window, picked a string of pearl-like buds and put them under my nose to suck. The thick smell was refreshing, and I was drunk at once! The tree became brilliant at once.

I like acacia flowers stained with morning dew, strings of white grapes swaying in the morning breeze, and wind chimes jingling in my heart like Yu Pei. For this reason, I often come to the office early, and I often miss spring.

That summer, the green leaves of Sophora japonica crowded in front of the window, shielding me from the hot sun like a canopy. My room is the coolest in the whole office building, and there is no sulking at all. In autumn, colorful leaves make the window look like a vivid picture. I used to design the scene in front of the window from different angles in spring, summer, autumn and winter, thinking about which day I would take it with my camera. Because I always felt that the scene in front of me belonged to me, photography was put on hold until one day I left this place and this office for some reason, and my desire for photography was not put into practice. This is my biggest regret. (Sun Yunhua)

15. What happened to my feelings for acacia trees in front of the window? What is the reason for the change?

16. The fourth paragraph says, "This tree became brilliant at once." What are the specific aspects of "glory"?

17. Paragraph 6 says, "This is my greatest regret". What does "this" mean? What philosophy of life has the author learned from it?

18. According to your real life, give an example to illustrate your understanding of the last sentence of the article.