According to some research it is estimated that about 20% of americans of the age of 12 are infected with the human papilloma virus.
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A vaccine works by stimulating the immune system to produce antibodies without actually infecting someone with that disease. They trigger the immune system to produce its own antibodies as though the body has been infected with the disease. But a vaccine will not make someone immune to a disease, it will simply help the body be able fight the infection better.
To much gas has build up in them? I guess
Pyroclastic materials are classified according to their size, measured in milli meters: dust (less than 0.6 mm [0.02 inch]), ash (fragments between 0.6 and 2 mm [0.02 to 0.08 inch]), cinders (fragments between 2 and 64 mm [0.08 and 2.5 inches], also known as lapilli), blocks (angular fragments greater than 64 mm), and bombs (rounded fragments greater than 64 mm).
The fluid nature of a pyroclastic flow is maintained by the turbulence of its internal gases. Both the incandescent pyroclastic particles and the rolling clouds of dust that rise above them actively liberate more gas. The expansion of these gases accounts for the nearly frictionless character of the flow as well as its great mobility and destructive power.
Pyroclastic flow, in a volcanic eruption, a fluidized mixture of hot rock fragments, hot gases, and entrapped air that moves at high speed in thick, gray-to-black, turbulent clouds that hug the ground. The temperature of the volcanic gases can reach about 600 to 700 °C (1,100 to 1,300 °F). The velocity of a flow often exceeds 100 km (60 miles) per hour and may attain speeds as great as 160 km (100 miles) per hour.
To learn more about Pyroclastic materials here
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Answer:
Actually, D is the correct answer
