Using Fonts

What is the right way to connect a font using a file?

A)

@import url('my-font.otf');

B)

.block {  
  @font-family { 
    url('my-font.otf'); 
  }
}

C)

@font-family { 
  url('my-font.otf'); 
}

D)

@font-face {
  src: url('my-font.otf');
}

E)

.block {
  font-family: 'my-font.otf';
}