Could anyone helps me to check whether I use commas correctly in these sentences? Thank you!!!
1.I had chance to observe 10B6 class, consisting of 29 students.
2.The final scientist’s name, Maria Curie, was used to lead-in.
3.He used technique network and then, asked students.
4.He spoke slowly, repeated the instructions several times, and used mime or hand signals when students don’t understand