Help me please ASAP I need to pass the test

In the practice of science, this type of reasoning is used to develop explanations.

Which enzymes break down carbohydrates?

The double bond between a carbon atom and two oxygen atoms (a molecule of carbon dioxide) has two characteristics. what are they? a.an ionic bond is formed between the oxygen and carbon atoms. b.four valence electrons are shared. c.two valence electrons are shared. d.valence electrons are shared between oxygen atoms.