Margarita built a sand castle. I made a cake.
A sand castle was built by Margarita. A cake was made by me.
Margarita was building a sand castle. I was making a cake.
A sand castle was being built by Margarita. A cake was being made by me.
Margarita had built a sand castle. I had made a cake.
A sand caslte had been built by Margarita. A cake had been made by me.