Read the following information and answer the question given at last:

Strong evidence from several studies has shown that individuals consuming fruits and vegetables rich in different flavonoids have a reduced risk of overall mortality and of several chronic diseases. According to new research from the University of East Anglia (UEA) and King's College London, eating high levels of flavonoids including anthocyanins and other compounds (found in berries, tea, and chocolate) may prevent type 2 diabetes, a disease whose initial stages is now affecting almost 40 percent of Americans age 20 and older.

Flavonoids, which are found in a variety of fruits and vegetables as well as in tea, red wine, chocolate and berries, are thought to boost health in part by combating oxidation, a process in which cell-damaging substances called free radicals accumulate. Oxidative damage can be caused by several factors, especially by those factors on the cellular level. It is suspected of increasing the risk of diabetes, heart disease, stroke and several other diseases …

Researchers studied almost 2,000 healthy women volunteers from Twins UK who had completed a food questionnaire designed to estimate total dietary flavonoid intake as well as intakes from six flavonoid subclasses. Blood samples were analysed for evidence of both glucose regulation and inflammation. Insulin resistance, a hallmark of type 2 diabetes, was assessed using an equation that considered both fasting insulin and glucose levels.

[Researchers] found that those who consumed plenty of anthocyanins and flavones had lower insulin resistance. High insulin resistance is associated with Type 2 diabetes, so what we are seeing is that people who eat foods rich in these two compounds - such as berries, herbs, red grapes, wine - are less likely to develop the disease.

Requirements:

(a) Is this particular study that was cited in the article observational or experimental? Explain your choice based on the extract given above.

(b) Identify the variable(s) of interest.

(c) Explain explicitly what a lurking variable is. Could there be a lurking variable in this study? If so, identify one plausible lurking variable and fully explain why it is a lurking variable.

(d) Is a conclusion from the study reflected in the title of the article appropriate? Justify your response.