title: Unable to build due to API update
body: <p>I have a problem with making an ActiveX program with C#.</p>
  <p>I'm trying to make a <strong>library</strong> that supports all program versions.</p>
  <p>For example, assuming there is a A() function in version 1.0.</p>
  <p>But in the next version 1.1, A() function is gone.</p>
  <p>So I can't build the code in version 1.1 because of the A() function. (IDE Error occurs)</p>
  <p><strong>I want to control all versions with one library.</strong></p>
  <p>Is there any ways to solve this problem?</p>
  <p>I used .NET Framwork 4.7.2 and Visual Studio 2019.</p>
  <p>I would appreciate your help.</p>
  <p>Thanks.</p>