The angel answered, "The Holy Spirit will come on you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God." (NIV)

Then the angel said to her, The Holy Spirit will come upon you, and the power of the Most High will overshadow you [like a shining cloud]; and so the holy (pure, sinless) Thing (Offspring) which shall be born of you will be called the Son of God. [Exod. 40:34; Isa. 7:14.] (AMP)

And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God. (KJV)