Which episode before "Summer Solstice" did they collectively stand up?

This is the fourth episode, and everyone is standing in front of the summer solstice.

Because the chemistry exam was too difficult, Fu Xiaosi, Chang Xia, Lu Zhiang and Cheng Qiqi stole the chemistry exam paper and shared it with the whole class. Because everyone scored high, the teacher found something fishy and forced him to ask who was the mastermind in the class. Chang Xia doesn't want to embarrass the class. She clenched her fist and gritted her teeth to take on all the responsibilities. Fu Xiaosi hold down the long summer, bravely stood up, put all the responsibility on themselves. Looking at Fu Xiaosi's courage, Chang Xia also stood up and admitted his mistake. Lu Zhiang couldn't stand the teacher's overbearing style, and stood up and confronted the teacher. Under the leadership of these three people, all the students in the class bravely stood up and confronted the teacher. The teacher looked at the determined eyes of the whole class, angrily punished the whole class for copying the paper for one hundred times and left. Perhaps this is the so-called love of classmates, knowing that you will be punished, but you still have to shoulder the responsibility bravely with all your companions.