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Option 2 seems right to me.

i will knock on the window ask a teacher to help and then go to the bathroom

I will choose option 2.

Since she needs to go to the bathroom, I guess she can't hold it longer. So she has to ask for help from another teacher.

Since she has 20mins, she would not be able to hold it for to long. She has to seek for help from other teachers.

I go with this option

I'll choose this option.

I go with this option.

It's best she knocks on the teachers windows for help.

I choose this option

Knocking on the teachers door should be the right way to go.

I will guess option 2 to knock on the nearest window.

I also think option 2 would the best, as option one is not a good one, she might not be able to hold that long. And option 3 to leave the kids alone for even one second can be disastrous.