並木道って英語でなんて言うの？

Both ways are correct! Because I am a language nerd, I put both of these phrases into some online tools which show how often they are used in books. Before 1900, "row of trees" was used much more frequently than "line of trees". Then, for about 50 years, "row of trees" and "line of trees" were used with equal frequency. Now, "line of trees" is a little more popular. But you could use either one, and everyone would understand you perfectly!

Both of these answers have the same meaning. Usually lines/rows of trees are planted and not naturally occurring.

Both of these phrases are correct and mean the same thing. The word line and row basically mean the same thing.

The phrase "a row" refers to a horizontal line of something. Therefore, "line" and "row" means the same thing. I hope that this helps! :)

A row or line means exactly the same thing so either of these phrases would be fine to use you could say 'I saw a row of trees by the road' or 'I saw a line of trees by the road'

There is very little difference between these to ideas. The biggest is that a "line" can be described as a geometrical term for any two points that are connected. While a row is only objects or nouns. The trees are in a row. Here is a row of eggs. There is a line between point A and point B.

There is no real difference between these ideas. Either one expresses the idea of trees in a straight line in a garden or as part of some landscaping. Generally, I would use "row" instead of "line" when talking about things in a straight line. For example "row of bushes" or "soldiers marching in a row". Both of these express the idea of things in a straight line. I would use the word line when describing a course such as "run a straight line" or "the plane flew in a straight line".