C # problem

Under what conditions will this test pass?

[Fact]
public void NewTest()
{
var a = new A();

a.GetType().GetField( "b" ).SetValue(a, 83);
a.GetType().GetField( "c" ).SetValue(a, 42);

Assert.Equal(ab, ac);
}
upd: 5 correct decisions have already been written in the comments, if it is interesting to evaluate your knowledge and imagination - do not look prematurely there.