The three correct statements that are true for all biomolecules are:
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They have hydrogen elements. - All biomolecules contain hydrogen atoms.
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They have a carbon backbone. - Most biomolecules, particularly organic molecules like carbohydrates, proteins, lipids, and nucleic acids, have a carbon backbone, although some exceptions may exist (e.g., certain small molecules).
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They have covalent bonds. - Biomolecules are primarily composed of atoms that are connected by covalent bonds, which are essential for forming the structure and function of these molecules.
The statement "They have nitrogen elements" is not universally true as not all biomolecules contain nitrogen (for example, many carbohydrates do not).