Here something that might help
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Most scientists believe that for half of </span>Earth's<span> 4.6-billion-year history, the</span>atmosphere<span> contained almost no </span>oxygen<span>. Cyanobacteria or blue-green algae became the first microbes to produce </span>oxygen<span> by photosynthesis, perhaps as long ago as 3.5 billion years ago and certainly by 2.7 billion years ago.</span>
B is the correct answer to your question
The thickness of the uterine lining , becomes very thick...because when the level of hormone progesterone reaches its highest levels. according to Dr.X on yahoo answers.
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