Fill in the blanks with the most appropriate option:-

The small kid has learnt her ________ very quickly.

lesson

The most appropriate option to fill in the blanks is lesson.

The sentence "The small kid has learnt her lesson very quickly." means that the small kid has learned something very quickly. The word "lesson" refers to something that is taught, and it is the most appropriate word to use in this context because it accurately reflects the meaning of the sentence.

The other options are not as appropriate.

• To lessen something means to make it smaller or less in amount. This does not make sense in the context of the sentence, as the small kid is not making her lesson smaller or less in amount.
• Tutorials are a series of lessons that are typically given by a teacher or instructor. This does not make sense in the context of the sentence, as the small kid is not taking a tutorial.
• Classes are a group of students who are taught together by a teacher. This does not make sense in the context of the sentence, as the small kid is not taking a class.