The building block of anthraquinone glycosides is acetate

Anthraquinones (AQs) are derived from anthracenes and have two keto groups, mostly in positions 9 and 10 (Fig. 1). The basal compound, anthraquinone (9,10-dioxoanthracene), can be substituted in various ways, resulting in a great diversity of structures. AQs are widely distributed in the plant kingdom (Table I; cf. Zenk and Leistner, 1968). AQs appear in oxidized and reduced (anthrones) form as well as in a free or a combined (glycosidic) state. They are isolated from various plant parts, that is, leaf, stem, root (the principal site of accumulation), pod, seed, coat and embryo, but not endosperm. Naturally occurring AQs possess dyeing and/or pharmacological (purgative) properties.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

gold is my favorite solid.