Extract the answer to the following question from the movie plot. If the question isn't answerable, please output "Can't answer". Question: Who plays Dr Serena Koogan in Terminator Salvation? Title: Terminator Salvation Movie plot: In 2003, Dr. Serena Kogan (Helena Bonham Carter) of Cyberdyne Systems convinces death row inmate Marcus Wright (Sam Worthington) to sign over his body for medical research following his execution. One year later, the automated Skynet system is activated, becomes self-aware, begins to perceive humans as a threat, and eradicates much of humanity with nuclear weapons in the event known as "Judgment Day". In 2018, John Connor (Christian Bale) leads an attack on a Skynet base, where he discovers human prisoners and schematics for a new type of Terminator, incorporating living tissue (The T-800). He is the only survivor of the assault after the base is destroyed in a nuclear explosion. Following Connor's departure, Marcus emerges from the base's wreckage and begins walking towards Los Angeles, after taking the clothing from a Resistance soldier, who died in the explosion. John returns to Resistance headquarters, located aboard a nuclear submarine, and tells General Ashdown (Michael Ironside) of his findings. Meanwhile, the Resistance has discovered a radio signal believed to have been an order to shut down Skynet's machines. Working on this intelligence, the human militia plan to launch an offensive against the Skynet base in San Francisco in four days; in response to an intercepted "kill list" created by Skynet with a plan to terminate the Resistance's command staff. John Connor learns he is second on this list, following Kyle Reese. The Resistance leaders are unaware of Kyle's importance, but John knows Kyle will eventually go back in time and become his father. John returns to his base and meets with his pregnant wife Kate (Bryce Dallas Howard) and his second-in-command Barnes (Common). Arriving at the ruins of Los Angeles, Marcus sees a T-600 Terminator and yells at it grasping its attention, but before Marcus is killed he is saved by Kyle Reese (Anton Yelchin) and a mute child named "Star" (Jadagrace Berry). Kyle then signs to Star and she sets off a trap for the T-600 that kills it off. After such, Kyle...
A:
Helena Bonham Carter