I'm learning C #, I do not know much about IDE, so it can be silly.
I needed to create a class library, the "teacher" uses the VS 2015, I use the 2017, he chose the only library of classes that I had, I had several (standard, framework, portable, windows universal) I chose the "standard" I assumed it would be the common one.
I need to add a directive "Using System.Data;" And after that, add "Using System.Data.SqlClient;" However, I do not know why it is a mistake, and it tells me that "the use of the directive is not necessary"
I do not know what the error may be, I'm following a course, and the one who dictates it has the same as me, everything, but he does not make mistakes. I leave screenshots.
I need to be able to use the "DataSet" I'll be attentive, thank you.