instruction:
In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.
question:
Question: What holds ionic and covalent compounds together? Answer: electrostatic attractions
answer:
Electrostatic attractions holds ionic and covalent compounds together.

question:
Question: Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of what exist? Answer: equilibrium
answer:
Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of equilibrium exist.

question:
Question: The first photosynthetic organisms were not plants, but types of what that lived in the water? Answer: bacteria
answer:
The first photosynthetic organisms were not plants, but types of bacteria that lived in the water.