When tossing a coin, the coin can come up heads or tails. Suppose we flip 2 coins. Our first coin is a fair coin, and we're going to denote the outcome by X1. So the chance of X1 coming up heads is half. But now we branch into picking a coin based on the first outcome. So if the first outcome was heads, we pick a coin whose probability of coming up heads is going to be 0.9. The first coin flip might also come up tails, in which case we pick a coin which with 0.8 probability will once again give us tails, conditioned on the first coin flip coming up tails. What's the probability of the second coin flip coming up heads? O A. 0.25 O B. 0.55 O C. 0.3125 O D. 0. 125