The answer is all of the above. Please see: Isaiah 7, Matthew 1 and Luke 1. Here is a portion of D. James Kennedy and Jerry Newcombe, The Real Messiah: Prophecies Fulfilled:

        A young American minister, freshly minted from a theological seminary, went out to take his first pastorate. It was a little church out in the country in an area mostly populated by Scandinavian folk, and the young man was filled with great zeal and hope.
        He noticed that in the area there lived an elderly gentleman who apparently did not attend church at all. One day the young pastor invited him to attend, and he refused. The next week he invited the man again and finally he agreed. He picked him up and drove the man to church. His sermon happened to be on the same topic of this chapter, which is the Virgin Birth of Christ. As he was driving him back home, the minister made a foolish mistake only made by very young preachers. He said, "Well, how did you like the sermon?"
        The elderly man was silent for a while, but he finally said, "Well, now, young man, if there was a young girl that got herself pregnant today, and then you were told that it was a virgin birth, would you believe that?"
        The young pastor was quiet for a moment, and then he said, "Well, if that Child grew up to live a sinless life, the only life that men have never been able to find fault with; if He worked numerous extraordinary miracles; if He raised the dead; walked on  water; and if He Himself having been crucified, rose again from the dead and then ascended into heaven, yes, I would believe that He was Virgin born."

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