System.Activities/System.ComponentModel reference not found in Visual Studio

Good day.

Following this UIPath Resource:
Creating a custom activity

You need to do the following steps:
1.Open Visual Studio
2.Start New Project
3.Pick Visual C# -> Class Library
4.Go to References -> Add Reference…
5.Search and select System.Activities and System.ComponentModel
6.Now you can decide of you will use CodeActivity or NativeActivity
7.Override Execute method
8.Define the input and the output where is needed

I cannot find the required references?
I am using VS2017 community and creating a class library (.NET Framework)

Please advise?
Any other tutorials on creating custom Activities will be greatly appreciated.

Thank you.

Seems Like I found it in Assemblies.