Formal is used in situations that are more serious. For example when you're in a job interview or emailing your professor. It can also be used when you're speaking to someone you don't know very well and want to make sure you sound respectful.
Informal is used in a more relaxed, everyday situation. This includes conversations with friends, family and other people you know well.
I think it is D
Hope this help you!!
The correct answer is D. A concrete example is one that provides a clear situation in which the abstract idea, in this case the author's argument, is exemplified. This option not only prepares the reader for the example, but also gives specific details about what could be regulated.
I don’t know but i need points
