Explanation:

The correct answer is option 'D' - Peddler's sense of humour.

Introduction:
In the story "The Last Lesson" by Alphonse Daudet, the peddler plays a significant role in lightening the seriousness of the lesson. The story is set in Alsace-Lorraine, where the French language is being banned and replaced with German. The peddler, who is a local character, brings a sense of humor and liveliness to the otherwise somber atmosphere.

Peddler's sense of humour:
The peddler's sense of humour is evident throughout the story and helps to alleviate the seriousness of the lesson. Here's how his sense of humour lightens the atmosphere:

1. Peddler's funny comments: The peddler frequently makes funny and sarcastic remarks, which amuse the students and provide comic relief. For example, when he enters the classroom, he teasingly asks the students if they are attending a funeral. This light-hearted comment brings a smile to the students' faces and momentarily distracts them from the gravity of the situation.

2. Peddler's funny tricks: The peddler also performs amusing tricks, such as making his dog, Mouche, perform tricks and imitate a German officer. These tricks entertain the students and make them forget about the oppressive nature of the lesson. The peddler's ability to entertain through his tricks creates a jovial atmosphere in the classroom.

3. Peddler's witty conversation: The peddler engages in witty conversations with the students and the teacher, Monsieur Hamel. His quick-witted responses and clever remarks add a touch of humor to the otherwise tense situation. For instance, when Monsieur Hamel says that he himself is the culprit for not teaching them enough, the peddler jokingly suggests that it is a good thing for the students as they can now avoid doing their homework.

Conclusion:
In conclusion, the peddler's sense of humor plays a crucial role in lightening the seriousness of the lesson in "The Last Lesson." His funny comments, tricks, and witty conversations provide a much-needed break from the oppressive atmosphere in the classroom. The peddler's presence brings joy and laughter to the students, even in the face of adversity, making the lesson more bearable and memorable.