The electromagnetic wave is self propagating, what I mean by that is, an electric field generates a magnetic field at 90 degree phase angle, and the magnetic wave you get as a result generates the electric wave at the same phase angle. The interchange of electric to magnetic and vice versa continues and lets the electromagnetic waves to travel without any medium. Quite interesting, really!
I don't know a lot but I just did a class about this.
But to change perfect past tense completed in the past by changing the verb is or could be by replacing the verb with the action to was ,did ,before, ect. I think this might help
Answer: the speaker wants the audience to have a closer connection of the story and wants to readers to feel welcomed
Explanation: