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Propose a hypothesis of why the flu vaccine must be given every year but for most viral infections one or two doses of the vacci

ahrayia [7]

The flu vaccine changes every year. The flu vaccine is based on a predicted strain that is anticipated to be the most infectious that year. Thats why people who sometimes get the vaccination still get the flu, they don't have the antibodies for the strain they were infected with. Strains for viral disease don't change very much and usually the vaccination for them cover them well.

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3 years ago

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Naturally occurring solid mixture of one or more minerals and organic matter

alina1380 [7]

The naturally occurring solid mixture of one or more minerals and organic matter is known as a Rock.

A rock is a naturally occurring substances that is a solid mixture of one or more minerals together with organic matter.

<h2>Further Explanation;</h2>

Rocks are classified based on the chemical composition, texture and the way they are formed. One type of rock may change from one form to another through a rock cycle.
Rock cycle is the process through each various rocks change from one form to another, normally an interchange between the three major types of rocks.

There are three major classification of rocks:

<h3>Sedimentary rocks </h3>

Sedimentary rocks are types of rocks that are formed through accumulation of sediments at low temperatures in tectonic layers and sinks. These sediments includes; pebbles, shells, sand and other material fragments.
The sediments accumulates in layers and then harden into rocks over a period of time.
Examples of sedimentary rocks include; limestone and conglomerate

<h3>Metamorphic rocks</h3>

These are types of rocks that are formed as a result of changes that occurs due to intense heat and pressure under the surface of the earth. They result from action of heat and pressure on other rocks that pre-existed.
These types of rocks are characterized by shiny crystals, ribbon-like layers among other features.
Examples of metamorphic rocks are marble and gneiss

<h3>Igneous rocks </h3>

These are types of rocks that are formed as a result hardening and cooling of magma from volcanic eruptions. Magma may cool inside the earth or when on the surface of the earth as a result of volcanic eruptions. The lava from this eruptions cools and hardens to form metamorphic rocks.
Igneous rocks are glass-like and shiny with no crystals. They may also have tiny spaces and holes due to gas bubbles trapped during the cooling process.
Examples of igneous rocks include obsidian and basalt.
The three types of rocks may be further classified in terms of chemical composition, texture and formation.

Key words: Rocks, types of rocks, chemical composition

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