Entaglement

Go to move 11. This puzzle was from Sarah and Dads first round opener in the July tournament. Sarah just played C5 which is viewed as a fairly hefty mistake. However, its about to set her up to win the game. Dad pushes B4, presumably with the hope to trade bishop for bishop. 

1) why is this a losing trade for dad if he would have played this out? 

2) why is the choice he made instead a worse choice?

3) what are alternative responses he could have played to maintain his advantage?