Past simple passive or Present simple passive

Most ancient cultures had slaves, people who ​ ___________ and sold and forced to work without being paid (buy)

It is not just the way that cotton ​ ___________ which can involve slavery (grow)

The Great Pyramids in Egypt ___________ with slave labour (build)

After a huge campaign the slave trade ___________ in 1807 (abolish)

Some workers ___________ as little as 50 cents an hour (pay)

First, the British traders took goods to Africa, where these goods ___________ for slaves (exchange)

Finally, the products that the slaves had grown ___________ to England (ship)

Many people thin that cotton ___________ using slaves (produce)