Vaccination against the hepatitis a virus is unnecessary if you: select one:
a. are older than 35 years of age.
b. have a weak immune system.
c. received a hepatitis b vaccination.
d. have been infected with hepatitis in the past.

The correct answer is letter D

Is used to prevent infection caused by the hepatitis A virus. Hepatitis A is  a disease that affects the liver and is manifested by fever, general malaise, loss of  appetite, nausea, abdominal pain, jaundice and dark urine. The vaccine works by stimulating  organism to produce its own protection against the disease. The effect of the first dose of  vaccine appears about 14 days after its application and persists for at least 12 months.  

With the application of the booster dose, the protection of the vaccine can extend for 10 years.

changes in factors like average income and preferences can cause an entire demand curve to shift right or left. this causes a higher or lower quantity to be demanded at a given price. demand curves relate the prices and quantities demanded assuming no other factors change. it is important for consumers to know this information, because it is crucial for them to know what they can afford and can't afford. i hope this .