some of them is stack together vs some of them are stack together

Some examples from the web:

• So, another strategy we're following is actually to create wafers that we stack together, like an accordion, if you will.
• So the Exo is designed to be simply, basically like a coffee cup. They can actually stack together so we get extremely efficient transportation and storage out of them.
• So, we stack these wafers together, using the kidney cells.
• So we had a few Marshall stacks on the back wall and we just did the feedback together something like...
• The merged entity would be the only firm together with IBM to be present in all the elements of the technology stack.
• You should punch Mr. Stacks in the face so you can go play in the park together.

Some examples from the web:

• So, another strategy we're following is actually to create wafers that we stack together, like an accordion, if you will.
• So the Exo is designed to be simply, basically like a coffee cup. They can actually stack together so we get extremely efficient transportation and storage out of them.
• So, we stack these wafers together, using the kidney cells.
• There are stacks of maps and papers in the lair.
• There are stacks of maps and papers in the lair.
• And perhaps a green roof in the future, when we're further utilizing urban areas, where there are stacks of garden spaces.
• So we had a few Marshall stacks on the back wall and we just did the feedback together something like...
• The merged entity would be the only firm together with IBM to be present in all the elements of the technology stack.
• You should punch Mr. Stacks in the face so you can go play in the park together.