I couldn't buy a ticket because I had forgotten my money.
I couldn't buy a ticket because I forgot my money.
I forgot my money, and I couldn't buy a ticket.
I had forgotten my money and I couldn't buy a ticket.
The textbook that I'm teaching at school says the first and the third sentences are correct. Then what about the second and the fourth example?
Many thanks in advance, and I really appreciate everybody's help here. It's been a great help to me, indeed.
