I didn't reply your email because my email account had been hacked.
If my email account hadn’t been hacked, I would have replied your email.
She isn't at the conference because no one told her about it.
If someone had told her about the conference, she would have been there.
They have to take a test today, that's why they couldn't make the hiking trip yesterday.
If they didn’t have to take a test today, they could have made the hiking trip yesterday.
He can't raise the hamster if his parents don't allow him to. (Unless)
Unless his parents allow him to, he can't raise the hamster.
If I hadn't called him last night, he wouldn't have told me about his new job. (Had...)
Had I not called him last night, he wouldn't have told me about his new job.
I could have submitted the files successfully with your instructions. (But for)
But for your instructions, I could have submitted the files successfully.
They can't open the safe if they don't know the secret code. (Unless)
Unless they know the secret code, they can't open the safe.
I wouldn't have finished arranging the furniture if your brother had helped me. (Without)
Without your brother’s help, I wouldn’t have finished arranging the furniture.
I would make a lot of money if I invested in the real estate business. (Were)
Were I to invest in the real estate business, I would make a lot of money.