1)i should have studied harder. he studied/didn't study hard. 2) i should have joined the school band. she joined/didn't join the band. 3) i shouldn't have been so mean to jimmy. he was/wasn't mean to jimmy. 4) i shouldn't have chosen physics and chemistry. she chose/ didn't choose physics.
1) I should have studied harder.
He didn't study hard.
2) I should have joined the school band.
She didn't join the band.
3) I shouldn't have been so mean to Jimmy.
He was mean to Jimmy.
4) I shouldn't have chosen physics and chemistry.
She chose physics.