Fill in the blank (_) in the following sentence from the following choices.
Sentence: The medication made Justin sleepy but not Nelson because _ was susceptible to that side effect.

Choice 1: The medication made Justin sleepy but not Nelson because Justin was susceptible to that side effect.
Choice 2: The medication made Justin sleepy but not Nelson because Nelson was susceptible to that side effect.
Which of the choices is correct? Respond with only "1" or "2" and no additional text.
1
2. The medication made Justin sleepy but not Nelson because Nelson was susceptible to that side effect.