Answer:
D. There is no enough oxygen in the culture fluid
Explanation:
The cells in the test tube need to carryout one of the important metabolic processes of living organisms - respiration. The process involves the breakdown of glucose to generate energy for other metabolic processes in the cell.
Respiration can be carried out in the presence of oxygen (aerobic) or in the absence of oxygen (anaerobic). Human cells are primarily aerobic but can carryout respiration anaerobically in the presence of inadequate oxygen.
For aerobic respiration, glucose is broken down in the presence of oxygen to produce carbon-dioxide, water and energy in the form of ATP:

<em>In the absence of oxygen, the glucose becomes converted to lactic acid and a smaller amount of ATP is produced as compared to aerobic respiration.</em>
<em>Hence, lactic acid gradually builds up in the absence of oxygen due to anaerobic respiration.</em>
The correct option is D.
The answer is <span> b. a process of change through time.
Evolution is a process of change through time. It does not result in progress. Natural selection, one of the mechanisms of evolution, can result in progress and </span>cause some organisms to develop characteristics they need. But generally speaking, natural selection is not the only mechanism of evolution. Other evolutionary mechanisms, such as genetic drift, mutations, migration, can in some cases have a harmful outcome.
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