Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Three isoforms of human plasma apolipoprotein E (apoE) are ligands to lipoprotein receptors and influence in different manner the synthesis and catabolism of pro-atherogenic triglyceride-rich lipoproteins. Among three isoforms, the apoE4 isoform is associated with increased frequency of atherosclerosis and Alzheimer's disease (AD). The conformational transitions of beta-amyloid (Abeta) influenced by apoE and serum amyloid P (SAP) component are key events in AD development, the accumulation of intermediate diffusible and soluble oligomers of Abeta being of particular significance. SAP and apoE, in a different manner for the three isoforms, serve as "pathological" chaperones during the aggregation of Abeta considered as a conformation-prone process. In turn, apoE consisting of two domains self-associates in solution and intermediate structures differently populated for the three isoforms exist. The different structures of the three isoforms determine their different distribution among various plasma lipoproteins. The structural and metabolic consideration of the common apoE pathway(s) in two pathologies assumes four molecular targets for AD correction: (i) inhibition of the accumulation of diffusible soluble Abeta oligomers; (ii) inhibition of apoE synthesis and secretion by astrocytes, in particular, under lipid-lowering therapy; (iii) inhibition of the binding of apoE and/or SAP to Abeta; (iv) stimulation of the expression of cholesterol transporter ABCA1. 
 Question: Which ApoE isoform is associated with atherosclerosis and Alzheimer's disease?
apoe4 isoform

Context: Feia Lacus is one of a number of hydrocarbon seas and lakes found on Saturn's largest moon, Titan. 
 Question: What celestial body can Feia Lacus be found on?
titan

Context: In many cultures white is often associated with something positive. A white-collar job, for instance, is the kind of job many people look for, working with your brain and not your hands. White has a clean and pure image. That is why doctors, dentists, and nurses usually wear white uniforms. Babies are dressed in white at baptisms and brides wear white wedding gowns at weddings. White in these cases is the symbol of innocence or purity. Sometimes white is used in expressions that are not good. "Whitewash" is one such expression. At first, "whitewash" meant to paint over something with white paint to make it look better. However, it means something different today: to hide or to cover up mistakes or failures. A "white elephant" is another example of white used in a negative way. In ancient Thailand, a white elephant was regarded as a sacred animal, but it was very expensive to keep. The kings of those days presented a white elephant to the people they wanted to ruin. Once they received this holy, royal animal as a gift, they were not allowed to sell or kill it. Today, a "white elephant" means something that is big, useless, and unwanted. In America, when people want to get rid of their furniture or clothes, they often have a "white elephant sale". 
 Question: Which expression has an historical background?

white elephant.