The answer is (b): the electron beam will be deflected downward, as seen in a series of pictures obtained by clicking on the photograph below.
When a positive current flows in a wire, if you point your thumb in the direction along which the current is flowing, your fingers will curl along the direction that the magnetic field points (going around in circles around the wire). Using this right hand rule, the direction of the magnetic field of the wire at the location of the CRT electron beam is into your video screen. Using the left hand rule, if you point your fingers in the direction that the electron beam is traveling (left to right, across your video screen) , then curl the fingers toward the direction of the magnetic field (into your monitor screen), your thumb will point in the direction that the electron beam will be deflected - downward.
