The correct answer is Metal.
Sound waves are vibrations which need medium to propagate. Higher the density of medium, the sound travels fastest. Sound travels fastest in solid than liquid and gas. Therefore, in this question sound will travel faster in metal because metal has higher density than air and water and it will not travel in vacuum as sound needs medium to travel.
That they are <span>caused by microorganisms.</span>
Answer:
The pressure differences on either side of the valve.
Explanation:
The heart valves open and close passively because of pressure differences on either side of the valve. When pressure is greater behind the valve, the leaflets are blown open and the blood flows through the valve. However, when pressure is greater in front of the valve, the leaflets snap shut and blood flow is stopped.
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Answer:
c. mosses
Explanation:
Primary succession occurs in places that have never been occupied by a community. Simple species are established first, as they help enrich the soil, allowing other species to become established. The first organisms to appear in areas of primary succession are often pioneer species such as mosses or lichens.
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