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Three influenza pandemics occurred during the 20th century: the 1918-19 “Spanish flu,” the 1957-58 “Asian flu,” and the 1968-69 pandemic or “Hong Kong flu.” In 2009, the World Health Organization (WHO) declared a global pandemic of H1N1 flu.
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The best answer to the question stated above is letter C.<span>The moon's orbit must cross the plane of the ecliptic.</span>
>><span>Solar eclipses happen when the Moon moves between Sun and Earth, blocking the Sun's rays and casting a shadow on Earth.
>></span>Solar eclipses<span> can happen only during a </span>new Moon<span>.
>>E</span><span>arth's orbit is called the ecliptic plane as the Moon's orbit must cross this plane in order for an eclipse (both solar as well as </span>lunar) to occur
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Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO2 and other heat-trapping gases to the atmosphere. These greenhouse gas emissions have increased the greenhouse effect and caused Earth's surface temperature to rise
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Innate immunity is a non-specific immune system which provides defence against any pathogenic microorganism in early stages. It includes physical barrier such as skin, chemical barriers such as saliva, tears, et cetera, phagocytic cells such as macrophages, et cetera.
Acquired immune system is the one which develops after exposure to pathogen or antigen. It is highly specific in nature. It includes B-lymphocytes and T-lymphocytes. It includes the production of antibodies.
Vaccines are used to develop acquired immunity in people. The process is termed as vaccination or immunisation. Heat-killed or weakened pathogen or antigen is inserted into a person after which a person develops antibodies and memory cells against that pathogen or disease. So, the immune system acts more vigorously against that pathogen in secondary infection.
Thus, a person becomes immunised.
