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The correct choice is polar solvents. Polar solvents, like methanol and ethanol, have molecules with a significant dipole moment, meaning they have a positive and a negative end due to the uneven distribution of electron density. This characteristic allows them to form hydrogen bonds with water molecules, making them mix readily with water.

In contrast, nonpolar solvents lack this dipole moment and do not interact favorably with water, which is why they do not mix well. Hydrophobic substances are those that repel water and do not dissolve in it, further supporting why they do not belong in the context of substances that mix well with water. Mixing substances refers more specifically to the ability to dissolve completely in a solvent, which is mainly seen in polar solvents when it comes to water.