Answer:
Your answer is probably A). If you find a fossil of an armored fish in layer A, and you find a fossil of a trilobite in layer B (five layers deeper), then you can safely assume that the trilobite is older than the armored fish.
By process of elimination you can find the right answer. We know for a fact that carbon is found in all living organisms. That is why we talk about carbon based life forms. So the first statement cannot be true. You can figure out how many Valence electrons an element has by looking at the group number. The group number of carbon is 4 so the 2nd statement cannot be true. We know that carbon does bond with other elements because it is not a noble gas and therefore must be able to form compounds.
This means the answer must be they can form up to four covalent bonds
O2 (oxygen) is a covalent compound
Based on the CDC guidelines a person with a CD4+ cell count between 200-400 is regarded as being in <u>the second stage</u> of the HIV infection.
Acquired Immunodeficiency Syndrome
Acquired immunodeficiency syndrome (AIDS) is a condition caused by HIV (human immunodeficiency virus). AIDS is a chronic disorder and can become life-threatening for the infected person. The HIV viruses reproduce inside the host and while doing so they destroy the CD4+ immune cells which reduce the person's ability to fight against other diseases.
CD4+ cell count and AIDS
According to the CDC (U.S. Centers for Disease Control and Prevention), HIV infection is categorized into different stages based on the number of CD4+ cells.
- Stage 1: - CD4+ cell count is more than 500 per microlitre. There are no symptoms or AIDS-related conditions.
- Stage 2: - CD4+ cell count is more than 500 per microlitre. There are no symptoms or AIDS-related conditions.
- Stage 3: - The CD4+ cell count falls below 200 and AIDS-related symptoms and conditions are present.
Learn more about HIV infection here:
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When charged particles from the sun strike atoms in earth's atmosphere, it causes electrons to move to a higher energy state. When the electrons drop back to a low energy state they release light photons. This is what causes the Aurora lights
