Tsumego From Games 58

Status?  

Alex: White's group in the centre is quite weak (Black is thick on the right side of the board, not shown), so she would very much like to reinforce at a. However, the status of her group on the left side is in question. She has made the two marked forcing exchanges, but are they enough, or does White she still need to add a move?

• Attempts?
• Solution