What prohibits lipids from being a readily available energy source? fat must be broken down into fatty acids before being converted to glucose. lipids are structural components, so they are a last-resort energy source. lipids are only used to create enzymes, hormones, and antibodies. the conversion of fat to glucose is controlled by insulin.

Lipids are really hard to break down because they have strong bonds between the carbon atoms. Despite that through a series of metabolic processes they can be converted into fatty acids and then into glucose (and then converted into glycogen). 

From your list, it would be:
a. Fat must be broken down into fatty acids before being converted to glucose

The truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey

Ais the answer for you