Fill in the blank (_) in the following sentence from the following choices.
Sentence: I had less difficulty understanding this topic compared to the last lesson, because the _ was hard.

Choice 1: I had less difficulty understanding this topic compared to the last lesson, because the topic was hard.
Choice 2: I had less difficulty understanding this topic compared to the last lesson, because the lesson was hard.
Which of the choices is correct? Respond with only "1" or "2" and no additional text.
2
1. The sentence is about the topic being difficult to understand, not the lesson itself.