Which of the following is the most common site for the carcinoma of pancreas -
Most common site for carcinoma pancreas is head. The distribution as follows:

Head (75%) 
Body (15%) 
Tail (10%)

Ductal adenocarcinoma is the most common variety (90%)
Also know,
Risk factors for pancreatic Ca

Cigarette smoking is the most consistent risk factor.
As in other gastrointestinal cancers, diets high in fat and low in fibre, fruits and vegetables are thought to be associated with an increased risk.

Other risk factors are :
Chronic pancreatitis
Diabetes
Obesity
Alcohol abuse or cholelithiasis are not risk factors for pancreatic cancer.
Head
Ampulla
Body
Tail