Why Did the Participants in Raymond Et Al

Why did the participants in Raymond et al. (1992) study on attentional blink, have a difficult time identifying the probe when it was placed 2 to 6 letters after the target stimulus?

A) The participants were blinking after the target, so they could not see the probe.
B) The probe was below the threshold level of detection.
C) The target stimulus was of a different color and interfered with the processing of subsequent letters.
D) The participants were focused on identifying the target stimulus and could not attend to the probe.