Smoke is a type of mixture where gases, liquids, and solids are all combined. Option 1 states that smoke is a mixture of a solid and a gas, which is partly correct because smoke does contain solid particles suspended in a gas. Therefore, option 1 is partially correct but does not fully describe the composition of smoke.

Option 2 states that smoke is a mixture of two gases, which is not accurate. While there may be gases present in smoke, it is not solely a mixture of gases.

Option 3 suggests that smoke is a mixture of a liquid and a gas. Although smoke can contain water vapor or other liquid droplets, it is not solely made up of a liquid and a gas.

Option 4 accurately describes smoke as a mixture of gases, liquids, and solids. Smoke is often created through the combustion of materials such as wood or tobacco, which produces carbon particles (solid), water vapor or other liquid droplets, and gases such as carbon dioxide. Therefore, option 4 is the correct answer.