If Mary planned to consummate her marriage to Joseph, why was she confused when the angel told her she would bear a son?

The current top answer to [this question](https://christianity.stackexchange.com/questions/61914/why-did-mary-need-to-remain-a-virgin-during-pregnancy-according-to-those-who-den) (the answer given by SLM) asserts as a matter of fact that 1. Mary and Joseph consummated their marriage 2. Mary never took a vow of chastity 3. Jesus was born in the normal, "human" way (meaning that the birth destroyed Mary's physical virginity) This question is about points 1 and 2. If these statements are true, why is Mary surprised when the angel tells her she will conceive and bear a son? "How can this be, seeing I am a virgin?" Luke 1:34 NIV. Mary was already betrothed when the angel came to her. I imagine that if my wife had been visited by an angel a few weeks before our wedding and told she would conceive and bear a son, she would not be surprised (she may have been surprised by the visit itself, but not by the idea that she would become a mother). Indeed, we both expected pregnancy to result sometime after consummating our marriage and living together as husband and wife. So why did she respond this way? The [question submitted by Geremia](https://christianity.stackexchange.com/questions/67496/how-are-the-words-of-mary-in-luke-134-incontrovertible-proof-of-her-perpetual-v) as a possible duplicate is worth reading through, as is its top answer, but this is asking the opposite. The older question is asking Catholics how this phrase could mean that Mary is a perpetual virgin, whereas my question is asking Protestants why Mary would be surprised that she would bear a son, given that, according to them, she was already betrothed and planning on becoming a mother to Joseph's natural children.